Early life of Sherlock Holmes
Explicit details about Sherlock Holmes's life outside of the adventures recorded by Dr. Watson are few and far between in Conan Doyle's original stories; nevertheless, incidental details about his early life and extended families do construct a loose biographical picture of the detective.
An estimate of Holmes's age in the story "His Last Bow" places his birth around 1854; commonly, the date is cited as 6 January. However, on her website, Laurie R. King gives an argument for a younger Holmes, with a birth date somewhere between 1863 and 1868.
Holmes states that he first developed his deduction methods while an undergraduate. The author Dorothy L. Sayers suggested that, given details in two of the Adventures, Holmes must have been at Cambridge rather than Oxford and that "of all the Cambridge colleges, Sidney Sussex [College] perhaps offered the greatest number of advantages to a man in Holmes’ position and, in default of more exact information, we may tentatively place him there". His earliest cases, which he pursued as an amateur, came from fellow university students. According to Holmes, it was an encounter with the father of one of his classmates that led him to take up detection as a profession and he spent the six years following university working as a consulting detective, before financial difficulties led him to take Watson as a roommate, at which point the narrative of the stories begins.
From 1881, Holmes is described as having lodgings at 221B Baker Street, London, from where he runs his private detective agency. 221B is an apartment up seventeen steps, stated in an early manuscript to be at the "upper end" of the road. Until the arrival of Dr. Watson, Holmes works alone, only occasionally employing agents from the city's underclass, including a host of informants and a group of street children he calls the Baker Street Irregulars. The Irregulars appear in three stories, "The Sign of the Four", "A Study in Scarlet" and "The Adventure of the Crooked Man".
Little is said of Holmes's family. His parents were unmentioned in the stories and he merely states that his ancestors were "country squires". In "The Adventure of the Greek Interpreter", Holmes claims that his great-uncle was Vernet, the French artist. He has a brother, Mycroft, seven years his senior, who is a government official, who appears in three stories; he is also mentioned in one other story. Mycroft has a unique civil service position as a kind of memory-man or walking database for all aspects of government policy. Mycroft is described as even more gifted than Sherlock in matters of observation and deduction. However, he lacks Sherlock's drive and energy, preferring to spend his time at ease in the Diogenes Club, described as "a club for the most un-clubbable men in London."
It's unclear whether Holmes has any other siblings. In "The Adventure of the Copper Beeches", Holmes says, "I confess that it is not the situation which I should like to see a sister of mine apply for", leading some to suppose the existence of same. But he mentions this only to warn a woman in a case, taking her as his sister; therefore, this may be a mere figure of speech.