My little brother is. I can't stand him. He's only one year younger than me, but he still acts like a kid. I don't know if it's an asexual thing. He seriously makes it seem like sex is extremely bad and he does this thing where he makes inferences that I'm a pervert because I'm sexual. Are asexual people like this?
First of all, your "little brother" is 20-21, if I did the math right. He's not "little".
Second, if you're gay yourself, then give him support, guidance & help. Whether he's asexual, gay or whatever. As a brother should do.
If he's questioning his sexual orientation then help him. It matters not to me at all whether he's gay, straight, or bi. All is good.
What matters is that he recognizes & accepts whatever he really is. And that should be your own focus. As his evidently concerned older brother.
So first help him to recognize what he really is. And then support that outcome.
(BTW, I used to think I was asexual myself. Because I had no interest in women, and I denied my real sexual interest in men. So I came up with this "asexual" explanation, or excuse. Your younger brother may be doing the same thing.)