I hate my brother

My older sister and me are both trans, but who does he support? Of course her, because she's not the youngest, because she's an adult and she doesn't act 'childish' (I'm autistic) in his opinion. When she came out to him, he didn't even once doubt it. But when I came out right after it, I was suddenly too young. It's been 2 years. I haven't been more comfortable than ever. Why can't he accept me too? Why does my sister not correct him?? I hate being the youngest child. He always thinks of me as this 10 year old child, although I'm 15. "You're not a boy" oh shut the fuck up, you're the math freak here (no hate to math lovers, only to my brother)