What does 29 mean to Sherlock?
I found 2 references to to “twenty-nine” in ACD canon but neither of them really makes sense.
Maybe it’s an inside joke?
AX: Your Sherlock and Doctor Watson seem a little younger than they are usually shown on screen
MOFFAT: Well, the thing is, people keep saying, “Is this the youngest Sherlock Holmes?” You look at the Sherlock Holmes stories and the fact that we think of him as fifty is a product of the [previous films and television depictions]. It’s not true – he must be, in the first story, in his late twenties or early thirties. He’s referred to as a young man, even in the first story as a student. So he clearly could be twenty-nine in that first story… (x)