I think people feel liberated to say they’re gay these days, so there are much more people claiming to be gay than in previous decades. On the other hand, there’s still a lot of homophobes and also quite some biphobes around, so there’s probably a lot of bi people that present as hetero or even gay.
I’d assume that most people are at least a little bi, and that they’ll try that out in high school even if they later decide they won’t pursue it.