Personally, I think most of them are born that way. I've known young kids who showed homosexual traits. Sure enough, they grew up to realize they were gay. To me, showing signs at such a young age is at least SOME evidence that they were born that way.
But as was said before: Being gay doesn't mean they have to act on their feelings. I think it would suck to be in that position though (gay and not wanting to sin by doing what feels natural)