Question: Who was the youngest king?

List of British monarchy records


This List of British monarchy records lists various statistical records relating to the monarchy of the United Kingdom and its predecessors and constituents.
Summary

Reign of British monarchs

Longest
The longest reign of a British monarch is that of the current monarch, Elizabeth II (67years, 294days since 6 February 1952). The second longest reign is the 63 years 216 days of Victoria between 1837 and 1901. Queen Elizabeth II's reign became longer than Queen Victoria's on 9 September 2015.  The third longest reign (and longest of a King) was that of George III, who reigned for 59 years 96 days between 1760 and 1820.
James Stuart, the Old Pretender, was a pretender to the throne from 16 September 1701 until his death on 1 January 1766, a total of 64 years 108 days.
Prince Philip, Duke of Edinburgh has been the monarch's spouse (prince consort) since 6 February 1952, for a total of 67years, 294days, making him the longest-serving consort overall. The Queen consort with the longest tenure was Charlotte of Mecklenburg-Strelitz, who was George III's consort for 57years, 70days, between 1761 and 1818.
Prince Charles is the longest serving heir-apparent, Duke of Cornwall, and Duke of Rothesay, with a tenure of 67years, 294days, and Prince of Wales, with a tenure of 61years, 124days.
Margaret of Scotland, Countess of Kent was heiress-presumptive to William I of Scotland, Alexander II and Alexander III for a total of about 43 years, 14 days (her tenure as heiress-presumptive to Alexander II was also the longest single tenure at 26years, 274days). The longest-serving heir-presumptive (of either sex) was Robert II, who was heir-presumptive to Robert I and then David II for a total of 46 years, 353 days; he also served the longest single tenure (41years, 260days as heir-presumptive to David II).
Shortest
The shortest-reigning monarch was Lady Jane Grey who ruled for 9 days from 6 July until 15 July 1553 (although she was only proclaimed queen by the Lords of the Council on 10 July). Note: Jane's reign is disputed.
The king with the shortest definitively known reign was Edgar the Ætheling who ruled for 2 months, 12 days in 1066 before submitting to William the Conqueror. Some records indicate that Sweyn Forkbeard reigned for only 40 days in 1013-4.[1]
The queen consort with the shortest tenure was Yolande de Dreux, second wife of Alexander III, who was queen for 154 days in 1285 and 1286.
Elizabeth I holds the records for the shortest tenure of an English heiress-presumptive (almost 2 years as heir-presumptive to Henry VIII) and the shortest-serving English heiress-presumptive (and heir-presumptive of either sex) was Lady Jane Grey's sister, The Lady Herbert of Cardiff (13 days). 

The longest single tenure for a male heir-presumptive was Walter Stewart, Earl of Atholl, heir-presumptive to James II of Scotland for 5years, 144days; the shortest total tenure as a male heir-presumptive was George I (54 days).
Mary, Queen of Scots, was heiress presumptive from birth until her ascension to the throne at the age of 6 days.
Pretenders in Power
During the Middle Ages and the Mid-18th Century, a number of pretenders to the throne controlled all or a substantial portion of England and Scotland:
Empress Matilda: Daughter and only surviving child of Henry I of England, fought her cousin King Stephen for the throne. She held him prisoner from 7 April to 1 November 1141 and controlled a substantial portion of country from 1141 to 1148.
Henry the Young King, who was crowned junior king in 1170 at the age of 15, led a revolt against his father Henry II  for several months in 1173–74 and controlled much of England.
Louis VIII of France: Controlled the Southeast of England and later the whole country briefly in during the First Barons' War from 1215 to 1217.
James III and VIII sent his son Bonnie Prince Charlie to reclaim his kingdom and the latter controlled Scotland and Northern England for several months in 1745.
Edward Balliol was crowned king of Scotland in 1332 and was able to control some parts of it until 1336. His claim was recognized and supported by England.
Longevity

Monarchs
Longest-lived
The longest-lived British monarch and ruler is Queen Elizabeth II, the current monarch, who is now aged 93years, 220days, having surpassed her great-great-grandmother Victoria on 21 December 2007, who had held the record since 18 January 1901, surpassing her own grandfather George III.
The longest-lived male consort is her husband, Prince Philip, Duke of Edinburgh, who is 98years, 170days old
and is also the longest-lived male descendant of Queen Victoria.
Queen Victoria's longest-lived descendant overall was Princess Alice, Countess of Athlone (1883-1981) at 97 years, 312 days (Prince Philip would surpass her on 19 April 2019, and Queen Elizabeth II would pass her as longest-lived holder of a British royal title from birth on 28 February 2024). The longest-lived holder of a British royal title by marriage, and the oldest person in the history of the British royal family, was Princess Alice, Duchess of Gloucester (1901-2004) at 102 years, 319 days (Prince Philip would surpass her on 15 April 2024; Queen Elizabeth II would pass her age on 24 February 2029).
The longest-lived king was Edward Balliol of Scotland, who died at age 83 or 84 in 1367. Note: Edward Balliol's reign is disputed.
The longest-lived undisputed king was George III, who died at the age of 81 years, 239 days in 1820.
The longest-lived male ruler was Richard Cromwell who ruled as Lord Protector (1658-1659) who lived until the age of 85years, 282days.
The longest-lived queen consort and overall consort was Lady Elizabeth Bowes-Lyon, later known as the Queen Mother, consort to George VI, and mother of the current longest-lived British monarch, who was 101 years 238 days at the time of her death on 30 March 2002. Prince Philip would pass her as longest-lived overall consort in 4 February 2023.
Shortest-lived
The youngest Scottish monarch to die was Margaret, Maid of Norway, who died at the age of 7 years, five months, and 18 days in 1290.
The youngest English monarch to die was Edward V, who was most likely murdered after he was deposed, when he was 12.
Heirs apparent
The present Prince of Wales is the oldest heir apparent at 71years, 13days.
Prince William, Duke of Cambridge, is the oldest heir apparent to an heir apparent at 37years, 159days old.
The oldest heir apparent to an heir apparent to an heir apparent was Edward VIII (aged 6 years 213 days at the death of Victoria). Prince George of Cambridge is currently 6years, 128days old and would surpass Edward VIII on 20 February 2020.
Heirs presumptive
The oldest ever heir presumptive who died while in waiting was Sophia of Hanover, who lived from 14 October 1630 to 8 June 1714 (83years, 237days).
The oldest male heir presumptive was Ernest Augustus, King of Hanover who was displaced as next in line to Queen Victoria at the birth of his great-niece at the age of    69years, 169days.
Age of ascension
Oldest
The oldest monarch at the start of his reign was William IV who succeeded to the throne in 1830 at the age of 64 years 309 days. If the current Prince of Wales became the King today, he would be the oldest to do so at the age of 71years, 13days.
The oldest female monarch at the time of her ascension was Mary I, aged 37 years, 151 days when she became queen in 1553.
The oldest queen consort was Alexandra of Denmark, wife of Edward VII, who was aged 56years, 52days when she became queen in 1901. If Camilla, Duchess of Cornwall, were to become Queen consort (or possibly Princess consort) today, she would be the oldest to do so at the age of 72years, 133days.
Youngest
The youngest British monarch at the start of her reign was Mary, Queen of Scots, who became queen aged 6 days in 1542. The youngest king was Henry VI, who was 8 months and 26 days old at the time of his accession.
The youngest queen consort was Isabella of Valois, second wife of Richard II, aged  6 years 11 months and 25 days when she became queen in 1396.
Age differences, outgoing and succeeding monarchs
Greatest
The greatest age difference of an outgoing British monarch and successor was 54 years and 217 days between George II (born 30 October 1683) and his grandson George III (born 4 June 1738) who succeeded on the former's death on 25 October 1760.
Smallest
The smallest age difference of an outgoing British monarch and successor was 1 year and 171 days between Edward VIII (born 23 June 1894) and his brother George VI (born 14 December 1895) who succeeded on the former's abdication on 11 December 1936.
Marriage
Most marriages
Henry VIII was married six times, making him Britain's most-married monarch. The queen who was married the most times was Mary, Queen of Scots, who had three husbands.  The most-married queen consort was Catherine Parr, sixth wife of Henry VIII, who had four husbands.
Never married
William II, Edward V, Edward VI, and Elizabeth I all lived and died unmarried. In addition, Edward VIII was unmarried during his tenure as monarch, though he then married Wallis Simpson after his abdication.
Youngest
The youngest monarch to marry was David II, who married Joan, daughter of Edward II when he was 4years, 134days old in 1328.
The youngest female monarch at the time of her marriage was Mary II, who was 15years, 188days old when she married William III in 1677.
The youngest queen consort was Isabella of Valois, who married Richard II when she was 6years, 358days old in 1396.
Oldest
The oldest monarch at the time of his first marriage was William IV, who was 52years, 324days old when he married Adelaide of Saxe-Meiningen in 1818.
Mary I was the oldest queen at the time of her first marriage, aged 38years, 157days when she married Philip of Spain in 1554.
When second or subsequent marriages are included the oldest monarch at the time of his marriage was Edward I, whose second marriage was to Margaret of France in 1299 when he was 60years, 83days old and she was no more than 20.
The oldest queen consort at the time of her marriage was Maud, Countess of Huntingdon, who married David I when she was around 40 years old.
Longest
The longest marriage of a British sovereign is between Elizabeth II and Prince Philip, who have been married since 20 November 1947, making their marriage 72years, 7days old.
Shortest
The shortest marriage is between Alexander III of Scotland and Yolande, who were married for 4 months and 19 days from 1285-1286 until the former's death.
Children
Most
The British monarch with the most children was Henry I, who had 29 children (5 legitimate).
The British monarch with the most legitimate children was George III, who had 15 children with Queen Charlotte of whom 13 reached adulthood.
The Queen regnant with the most children was Queen Victoria who had 9 children of whom all reached adulthood.
The Queen regnant with the most pregnancies was Anne, who had 17, but only 5 resulted in live-born children (two of whom survived past the age of one, one reached the age of two, but all of them died before their mother). 
Age of parents
At 19, Henry IV is the youngest King to father a child, prior to his accession.
The youngest queen regnant to give birth is Mary II, who gave birth to a stillborn child in 1678, prior to her accession, when she was just 16. 
The youngest mother to give birth to a monarch was Lady Margaret Beaufort, wife of Edmund Tudor, who was 13 years and almost 8 months when she gave birth to Henry VII in 1457.
The oldest King to become a father was Edward I, who fathered his last child, Eleanor, in 1306, when he was 66, almost 67 years old.
The youngest Queen Consort to become a mother was Eleanor of Provence, who gave birth to Edward I, in 1239, when she was around 16.
The oldest Queen Consort to become a mother was Eleanor of Aquitaine, who gave birth to John, in 1166, when she was 44.
Physical attributes
Tallest
The tallest measured British monarch was Edward IV, whose skeleton measures 6'4½" (1.94m). Records indicate that when fully clad in armour he would have been about 6'7" (2 metres), an exceptional height for any man in the 15th century.
Both Edward Longshanks and Richard the Lionheart were also considered unusually tall for the mediaeval period - although contrary to popular belief, 'Longshanks' was not called that due to the length of his legs, but his arms; they were over a yard long (91cm), though there is no evidence to suggest they were particularly disproportionate to the rest of his body.
The tallest queen was Mary, Queen of Scots, who was around 6 feet tall, which was exceptionally tall for a woman of this time.  Her Stuart descendants Mary II and Anne were both of comparable height.
Shortest
The shortest British monarch in adulthood was most likely Queen Victoria, who stood only 5' (1.52m) when in her 30s, and was possibly an inch or two shorter towards the end of her life.
See also
Lists of monarchs in the British Isles
Records of Prime Ministers of the United Kingdom