What? If you have same-gender desire as a teenager, that's not something that really goes away... Sure, most people end up feeling mostly straight attraction. But sexuality is a continuum, like Butterfly said.
(Off topic, perhaps, but please don't use the word "homosexual", it's considered outdated and rude.)

Anyway, it's perfectly normal to start having or recognizing same-gender desire later in life. Many people aren't comfortable or in touch enough with their feelings when they first start to grow up. You may still consider yourself straight still, if you want to, but know that there is a place for you in the bi community, too!