Many homosexuals become certain about their sexual orientation during adolescence. There are 12-year-old boys who know definitely they are gay.
In a homophobic society this may be a very traumatic experience (see the story of Jamie Nabozny). Martin 1982 describes the problems of the coming out of a gay adolescent.
The reasons for homosexuality are unknown, but it is already clear that experiences in preadolescence and adolescence don't cause homosexuality - indeed, children as young as four can demonstrate behavior that reveals their sexual orientation
A study by Augelli & Hershberger 1994 gives the following numbers:
First aware ness of sexual orientation: age 10
Self-labelling: age 15