Question: How old was Rose Hartwick Thorpe when she wrote the poem she would be largely remembered for writing? 

Context articles: Sir John Piers, 6th Baronet
Curfew Must Not Ring Tonight
Rose Hartwick Thorpe
Tadashima Akiyama
Hall–Mills murder case
Harriet Taylor Mill
Harold Drinkwater
Richard Swann Lull
Misao Fujimura
Friedrich von Hefner-Alteneck

Sir John Bennett Piers, 6th Baronet, of Tristernagh Abbey, (1772 – 22 July 1845) was an Anglo-Irish baronet, now largely remembered for his part in a major scandal of the early 19th century and for being the subject of an early poem by John Betjeman, "Sir John Piers".
Curfew Must Not Ring Tonight is a narrative poem by Rose Hartwick Thorpe, written in 1867 and set in the 17th century.
 It was written when she was 16 years old and first published in "Detroit Commercial Advertiser".
Rose Hartwick Thorpe (July 18, 1850 – July 19, 1939) was an American poet and writer, remembered largely for the narrative poem, "Curfew Must Not Ring Tonight" (1867), which gained national popularity.
 Other poems followed, among them being "The Station Agent's Story," "Red Cross," and "In a Mining Town."
 Although a busy and prolific author, she was ill for some years.
 In 1888, she and her family removed to San Diego, California, living in Rosemere, Pacific Beach.
Tadashima Akiyama, also called Akiyama of Tajima (但馬国秋山 , Tajima-no-kuni Akiyama , fl.
 16th century) , was a Japanese samurai of the Azuchi–Momoyama period who hailed from Tajima Province.
 A rather unknown figure, he is largely remembered for his defeat at the hands of the young Miyamoto Musashi, who was sixteen at the time.
 It has been concluded that Akiyama openly challenged Musashi.
The Hall–Mills murder case involved an Episcopal priest and a member of his choir with whom he was having an affair, who were murdered on September 14, 1922, in Somerset, New Jersey.
 The priest's wife and her brothers were accused of committing the murders, but were acquitted in a 1926 trial.
 In the history of journalism, the case is largely remembered for the vast extent of newspaper coverage it received nationwide; it has been regarded as an example of a media circus.
 It would take the Lindbergh kidnapping trial in the 1930s to eclipse the high profile of the Hall-Mills murder.
Harriet Taylor Mill (née Hardy; London, 8 October 1807 – Avignon, 3 November 1858) was a British philosopher and women's rights advocate.
 Her extant corpus of writing can be found in "The Complete Works of Harriet Taylor Mill".
 She is largely remembered for her influence upon her second husband, John Stuart Mill, one of the pre-eminent thinkers of the 19th century.
Dr Harold Drinkwater MD FRSE (1855-1925) was an English physician.
 He was usually referred to simply as Harry Drinkwater.
 He did much research into hereditary diseases but is largely remembered as an amateur botanist and exemplary artist of botanical subjects, creating over 200 exquisite plant portraits largely held by museums in Wales.
Richard Swann Lull (November 6, 1867 – April 22, 1957) was an American paleontologist and Sterling Professor at Yale University who is largely remembered now for championing a Pre-NeoDarwinian Synthesis view of evolution, whereby mutation(s) could unlock presumed "genetic drives" that, over time, would lead populations to increasingly extreme phenotypes (and perhaps, ultimately, to extinction).
Misao Fujimura (藤村 操 , Fujimura Misao , July 1886 – May 22, 1903) was a Japanese philosophy student and poet, largely remembered due to his farewell poem.
Friedrich Heinrich Philipp Franz von Hefner-Alteneck (April 27, 1845 in Aschaffenburg – January 6, 1904 in Biesdorf near Berlin) was a German electrical engineer and one of the closest aides of Werner von Siemens.
 He is largely remembered for the invention of the Hefner lamp, which provided the measure of luminous intensity used in Germany, Austria and Scandinavia from 1890 to 1942.
 The measure was called the "Hefnerkerze" (HK).
 The Hefnerkerze was superseded in the 1940s by the modern SI unit, the candela.