Oh yawn, the bi thing again. Not yawn to you, reader. Yawn to those people who have a bug up their ass about the bi people of the world.
There seems to be this idea that if you "end up with," meaning, I guess, have a monogamous, long-term relationship with, a same-sex partner, you were "really" gay all along, and if you have one with a different-sex partner you were "really" straight. By this rubric, I guess, to be really and truly bi, you must also be poly, and carefully maintain an exactly equal gender balance in your partners and dates, which yeah, is pretty rare, so no wonder they think bi-ness doesn't exist.
Of course, this is all bullshit. People can define their sexuality however they want. It's not like the DSM-Vor anything. You don't have to date or want to fuck ladies and dudes in exactly equal amounts to qualify. If bi feels right to you, then go with bi. And you can tell anyone who gives you shit that I told them to fuck off (because duh, obviously I am a very famous authority figure).
And! You are allowed to change your mind. Yes, it's true. You are allowed to have a fluid sexuality over the course of your life. I don't know why some people are so resistant to this idea. There's this narrative of like, "I've known since I was six," which is true for some people I'm sure, but for other people, things aren't so cut and dry.
For example, I grew up in a very conservative South Texas environment. Of my school of 3,000 kids, there were exactly 0 out kids. Kids who "seemed gay" got the shit beat out of them. In such a strongly heteronormative environment, I think people questioned their own heterosexuality only if their inner selves absolutely demanded it, so I don't know many bi-identified people from that place—only gay people and straight people.
But I think in a place where the options of gay, straight, bi, and asexual were presented without stigma, with none more normative than the other, TONS of kids would have decided they were queer. No research to back it up, but my gut says bi would be the most common sexual identity, with no outside forces. I know the whole scale of gayness idea is a little outdated, but to me that makes sense, and I doubt many people are truly 1s or 10s.
There is one beef with the label bisexual that I can get behind, which is that it reinforces the idea of a gender binary. This is true. Pan-sexual I think is preferred, but a lot of people get confused by that term so I also understand why some people stick with bi. What I said before about sexual orientation I think is even more true about gender: that if male and female identities weren't so strictly enforced, lots of people would find that these essentialized gender identities don't really describe them. Yay for queering gender!
But anyway, bi kid, you should go for it. Be bi! Good luck!