The birthyear of the character of Dr. Watson in the "Sherlock Holmes" stories is 1852; at some point in the 70s, he receives his medical degree and then joins the British Army as a surgeon. After an eventful military service, he suffers a bullet wound (the famous "Wandering Wound") at the Battle of Maiwand (1880, making him 28 at the time) and on top of that catches typhoid fever. He is discharged from military service with an invalid's pension and returns to Britain on the HMS Orontes either in '80 or '81. In 1881 (presumably at the age of 29), he moves in with Holmes in 221B Baker Street. The two then have numerous of the adventures described in the stories. In The Sign of Four, set in 1888, Watson, then at the age of 36, becomes engaged (for the first time as far as we can tell, though there is some controversy here regarding a wife being mentioned in The Five Orange Tips), and marries in 1889. We don't have any definite date of birth for the wife, Mary Morstan, later Watson, but we know she was 17 after 1878, putting her Y.O.B. at 1862 at the earliest, so she is at least a decade younger than Watson.

Now my question is: how representative would this sort of biography be of British men in the Victorian era, or more precisely of urban males with tertiary education? I think the popular belief about this time would be that women were to be married by their late teens or early twenties, and an unmarried man after the age of, say, 25-30 would be an oddity as well. We'd think this sort of extended adolescence, cohabiting in your 30s à la Friends or Big Bang Theory, is a motif of 90s and onward sitcoms. We wouldn't expect it in Victorian Britain.

Would this be a common biography? Or is it an unusual case that's simply needed to make the setting work?

edit: Adding additional information, fixing the typos.