It's true that some musicians/bands make decent money, but if you're seriously want to be in a metal band, realize that you are probably going to have to hold down a regular job besides the band. Most bands in this genre aren't going to make loads of money ever--some of them basically just break even after they've gone on tour.
Be serious about school now, try to get good grades so you can possibly get a scholarship to a school you would be interested in attending. Let your mom see that you are responsible--love the music you do and go to concerts (if she'll let you), but don't get screwed up on alcohol or drugs. If she sees that you are serious about your interest in music, she may relent a little on her own wishes for your future.
Have you ever thought of working for a record label (like Relapse or Metal Blade)? Do some research on it. It would be a career where you could scout out and work with bands, but you'd be getting a regular salary--something a lot of metal musicians don't have!