Some context: Rose Marie "Rosemary" Kennedy (September 13, 1918 - January 7, 2005) was the oldest daughter born to Joseph P. Kennedy Sr. and Rose Fitzgerald Kennedy, and was a sister of President John F. Kennedy, and Senators Robert F. Kennedy and Ted Kennedy. Rosemary experienced mental disabilities, and displayed less academic and sporting potential than her siblings; however, her disabilities were carefully concealed from the public by her prominent family. In her early young adult years, she also had behavioral problems. Her father arranged one of the first prefrontal lobotomies for her at the age of 23, but it failed and left her permanently incapacitated.
Kennedy was presented to King George VI and Queen Elizabeth during her father's service as the United States Ambassador to the United Kingdom. Her father presented his daughters instead of, more customarily, choosing about thirty young American debutantes, a decision which earned him favor in the press. Kennedy's "slowness" was also unconventional and daring for a debut (two of the queen's nieces remained in a mental hospital because they were mentally ill). Young women would practice the rather complicated royal curtsey, sometimes learning the performance at the Vacani School of Dancing near Harrods. She practiced for hours. She wore a gown made of white tulle with a net train and carried a bouquet of lilies of the valley. Her sister Kathleen was described as "stunning, but she was only a shadow of Rosemary's beauty." Just as Rosemary was about to "glide off" by stepping to the right, she tripped and nearly fell. Rose Kennedy never discussed the incident and treated the debut as a triumph. The crowd made no sign, the King and the Queen smiled as if nothing had happened, and it is unknown whether Rosemary was aware of her own stumble.  One Kennedy family biographer termed her "absolutely beautiful" with "a gorgeous smile." At twenty, she was "a picturesque young woman, a snow princess with flush cheeks, gleaming smile, plump figure, and a sweetly ingratiating manner to almost everyone she met." She enjoyed dancing, such as at her sister Kathleen's coming-out party. Kennedy's parents told Woman's Day that she was "studying to be a kindergarten teacher," and Parents was told that while she had "an interest in social welfare work, she is said to harbor a secret longing to go on the stage." The Boston Globe wrote requesting an interview which was refused, but her father's assistant Eddie Moore prepared a response, which Rosemary copied out laboriously, letter by letter:  I have always had serious tastes and understand life is not given us just for enjoyment. For some time past, I have been studying the well known psychological method of Dr. Maria Montessori and I got my degree in teaching last year.
How old was she at the time?
A: 
Some context: Lionel Barrymore was born Lionel Herbert Blythe in Philadelphia, the son of actors Georgiana Drew Barrymore and Maurice Barrymore (born Herbert Arthur Chamberlayne Blyth). He was the elder brother of Ethel and John Barrymore, the uncle of John Drew Barrymore and Diana Barrymore and the great-uncle of Drew Barrymore, among other members of the Barrymore family. He attended private schools as a child, including the Art Students League of New York. While raised a Roman Catholic, Barrymore attended the Episcopal Academy in Philadelphia.
Reluctant to follow his parents' career, Barrymore appeared together with his formidable grandmother Louisa Lane Drew on tour and in a stage production of The Rivals at the age of 15. He later recounted that "I didn't want to act. I wanted to paint or draw. The theater was not in my blood, I was related to the theater by marriage only; it was merely a kind of in-law of mine I had to live with." Nevertheless, he soon found success on stage in character roles and continued to act, although he still wanted to become a painter and also to compose music. He appeared on Broadway in his early twenties with his uncle John Drew Jr. in such plays as The Second in Command (1901) and The Mummy and the Hummingbird (1902), the latter of which won him critical acclaim. Both were produced by Charles Frohman, who produced other plays for Barrymore and his siblings, John and Ethel. The Other Girl in 1903-04 was a long-running success for Barrymore. In 1905, he appeared with John and Ethel in a pantomime, starring as the title character in Pantaloon and playing another character in the other half of the bill, Alice Sit-by-the-Fire.  In 1906, after a series of disappointing appearances in plays, Barrymore and his first wife, the actress Doris Rankin, left their stage careers and travelled to Paris, where he trained as an artist. He did not achieve success as a painter, and in 1909 he returned to the US. In December of that year, he returned to the stage in The Fires of Fate, in Chicago, but left the production later that month after suffering an attack of nerves about the forthcoming New York opening. The producers gave appendicitis as the reason for his sudden departure. Nevertheless, he was soon back on Broadway in The Jail Bird in 1910 and continued his stage career with several more plays. He also joined his family troupe, from 1910, in their vaudeville act, where he was happy not to worry as much about memorizing lines.  From 1912 to 1917, Barrymore was away from the stage again while he established his film career, but after the First World War, he had several successes on Broadway, where he established his reputation as a dramatic and character actor, often performing together with his wife. He proved his talent in such plays as Peter Ibbetson (1917) (with brother John), The Copperhead (1918) (with Doris), The Jest (1919) (again with John) and The Letter of the Law (1920). Lionel gave a short-lived performance as MacBeth in 1921 opposite veteran actress Julia Arthur as Lady MacBeth, but the production encountered strongly negative criticism. His last stage success was in Laugh, Clown, Laugh, in 1923, with his second wife, Irene Fenwick; they met while acting together in The Claw the previous year, and after they fell in love he divorced his first wife. He also received negative notices in three productions in a row in 1925. After these, he never again appeared on stage.
How old was he when he started acting on stage?
A:
age of 15.