I feel like my brother is ruining his life and it scares me but also makes me feel a little angry at him.
That's a lot to process. Why does his behavior make you scared and angry?
He is making his whole family worried, he's so immature. He still has not really decided on what's his major in college yet.
While it is completely normal to feel worry and annoyance at a family member, your brother doesn't need to settle on a college major right away. It's normal to be unsure about what you want to do in life when you're in college; consider giving your brother space to make his own choices.
I think he should have done it by now is all I'm saying.
Just be there to support him. You don't need to get scared or angry at him but I can understand why you are a little concerned.