Conan Doyle repeatedly said that Holmes was inspired by the real-life figure of Joseph Bell, a surgeon at the Royal Infirmary of Edinburgh, whom Doyle met in 1877 and had worked for as a clerk.Like Holmes, Bell was noted for drawing broad conclusions from minute observations.
Holmes frequently calls Watson's writing sensational and populist, suggesting that it fails to accurately and objectively report the "science" of his craft: Detection is, or ought to be, an exact science and should be treated in the same cold and unemotional manner.
You have attempted to tinge it ["A Study in Scarlet"] with romanticism, which produces much the same effect as if you worked a love-story ...
Some facts should be suppressed, or, at least, a just sense of proportion should be observed in treating them.
The only point in the case which deserved mention was the curious analytical reasoning from effects to causes, by which I succeeded in unravelling it.
An estimate of Holmes's age in "His Last Bow" places his year of birth at 1854; the story, set in August 1914, describes him as sixty years of age.