Question: Who was the youngest US president?

List of presidents of the United States by age

This is a list of presidents of the United States by age. The first table charts the age of each United States president at the time of presidential inauguration (first inauguration if elected to multiple and consecutive terms), upon leaving office, and at the time of death. Where the president is still living, their lifespan is calculated up to September 22, 2019. The second table includes those presidents who had the distinction among their peers of being the oldest living president, and charts both when they became and ceased to be oldest living.
Age of presidents


The median age upon accession to the presidency is 55 years and 3 months. This is how old Lyndon B. Johnson was at the time of his inauguration. The youngest person to assume the office was Theodore Roosevelt, who became president at the age of 42years, 322days, following William McKinley's assassination; the oldest was Donald Trump, who was 70years, 220days old at his inauguration. The youngest person to be elected president was John F. Kennedy, at 43years, 163days of age on election day; the oldest was Ronald Reagan, who was 73years, 274days old at the time of his election to a second term.
Assassinated three years into his term, John F. Kennedy was the youngest at the time of leaving office (46years, 177days); the youngest president to leave office at the conclusion of a normal transition was Theodore Roosevelt (50years, 128days). The oldest at the time of leaving office was Ronald Reagan (77years, 349days).
Born on May 29, 1917, John F. Kennedy was younger than four of his successors, the greatest number to date: Lyndon Johnson (8years, 9months, and 2days); Ronald Reagan (6years, 3months, and 23days); Richard Nixon (4years, 4months, and 16days); and Gerald Ford (3years, 10months, and 15days).
Born on February 6, 1911, Ronald Reagan was older than four of his predecessors, the greatest number to date: Richard Nixon (1year, 11months, and 7days); Gerald Ford (2years, 5months, and 8days); John F. Kennedy (6years, 3months, and 23days); and Jimmy Carter (13years, 7months, and 25days).
The oldest living U.S. president is Jimmy Carter, born October 1, 1924 (age 94years, 356days). He also has the distinction of having the longest post-presidency in U.S. history, currently at 38years, 245days. The youngest living president is Barack Obama, born August 4, 1961 (age 58years, 49days).
The shortest-lived president to have died by natural causes (thereby excluding John F. Kennedy and James A. Garfield, who were both assassinated) was James K. Polk, who died of cholera at the age of 53years, 225days; only 103 days after leaving office. The longest lived president was George H. W. Bush (94years, 171days).
Six U.S. presidents have lived into their 90s. The first to do so, John Adams, held the distinction of being the longest-lived president for nearly two centuries, from 1803 until Ronald Reagan surpassed his lifespan in October 2001.[1][2] The six nonagenarian presidents (one of whom is still alive) are:

John Adams
1735–1826
(aged 90years, 247days)
Herbert Hoover
1874–1964
(aged 90years, 71days)
Ronald Reagan
1911–2004
(aged 93years, 120days)
Gerald Ford
1913–2006
(aged 93years, 165days)
George H. W. Bush
1924–2018
(aged 94years, 171days)
Jimmy Carter
Born 1924
(age 94years, 356days)

Table

Notes


Oldest living U.S. presidents

Of the 44 persons who have served as president, 24 have become the oldest such individual of their time, with one, William Howard Taft, doing so twice. Herbert Hoover held this distinction for the longest period of any, from the death of Calvin Coolidge in January 1933 until his own death 31 years later. Lyndon B. Johnson held it for the shortest, from the death of Harry S. Truman in December 1972 until his own death only 27 days later. Theodore Roosevelt, at age 49, was the youngest individual to become the oldest living president; Jimmy Carter is the oldest to acquire this distinction, at the age of 94. Nine of these individuals have also had the distinction of being the oldest living vice president: John Adams, Martin Van Buren, Millard Fillmore, Andrew Johnson, Harry S. Truman, Lyndon B. Johnson, Richard Nixon, Gerald Ford, and George H. W. Bush.
On three occasions the oldest living president lost this distinction not by his death, but by the inauguration of a president who was older. Theodore Roosevelt (born 1858) lost this distinction when William Howard Taft (born 1857) was inaugurated, then, four years later, Taft lost it when Woodrow Wilson (born 1856) was inaugurated. Taft subsequently regained the honor, as he outlived the older Wilson. More recently, Richard Nixon (born 1913) ceased being the oldest living president when Ronald Reagan (born 1911) was inaugurated.
Altogether, eleven presidents have held this distinction while in office. In the cases of George Washington, William Howard Taft, Woodrow Wilson, and Ronald Reagan this occurred upon their inauguration as they were older than their living predecessors (or, in Washington's case, had no predecessors). In the cases of John Adams, Ulysses S. Grant, Theodore Roosevelt, Herbert Hoover and Richard Nixon, this happened at the same time as their becoming the only living president; in the cases of Andrew Jackson and Benjamin Harrison, the only other living president at the time was a younger predecessor, John Quincy Adams and Grover Cleveland respectively. By contrast, the president who acquired this distinction furthest from his time in office is Jimmy Carter, who had been retired for 37years, 314days.

Note
* Green text and an asterisk mark the inauguration date of a president older than any living ex-president. Other dates are the deaths of the then-oldest president.


Sources
Frank Freidel and Hugh S. Sidey, . The White House.
Robert S. Summers, . Internet Public Library.