Dr. Watson é.
Nos filmes e séries de TV, não há uma resposta clara. Nunca é realmente um problema e então os atores apropriados para os papéis sempre foram contratados, independentemente da idade.
Isso parece lógico, considerando que as histórias ocorreram durante um longo período (mais de 20 anos). Considerando-se um show como Sherlock salta de história para história, sua idade se torna um pouco sem sentido como se eles estivessem apontando para o realismo a este respeito, ele teria envelhecido (e de-idade!) Várias vezes.
Nos livros, se você estiver interessado, suas datas de nascimento foram especuladas.
An estimate of Holmes's age in the story "His Last Bow" places his birth in 1854; the story is set in August 1914 and he is described as being 60 years of age.
Alternativamente para o Sherlock:
In the very first story, A Study in Scarlet, something of Holmes' background is given. He was born in England either in the year 1854 or the year 1861... His older brother Mycroft, born either 1847 or 1854, whom the younger Holmes considered to be more intellectually gifted than himself, would spend much of his life on Her Majesty's Secret Service. The confusion in birth dates stems from the fact that, in "The Adventure of the Greek Interpreter", Sherlock refers to Mycroft as being "[s]even years [his] senior".
In A Study in Scarlet, Watson, as the narrator, establishes having received his medical degree from Barts and The London School of Medicine and Dentistry, the University of London in 1878, and subsequently being trained at Netley as a surgeon in the British Army. If one assumes that Watson entered the University of London around the age of twenty-five, he was born around 1853.
Como alternativa, para o Watson:
Various (extra-canonical) sources give Watson's birth date as 7 August, 1852 and his full name as Dr John Hamish Watson.
Essas datas colocariam Watson entre um e oito anos mais ou menos.