How old is Conan meant to be?
Of course, Conan's real age is the same as his age before he shrank. He was 16 at the time he shrank.

Conan does mention his age in the first volume of the manga in File 2, when he almost accidentally tells Ran that he is 16, instead of 6.


Later in the series, Conan's age is 7, as he has experienced a birthday. 

Conan is also around the same size as other kids that age, which is probably why he was put in class 1-B when he started going to grade school. In Japan, first year grade school students are between ages of 6 and 7.