I'm a senior in high school as well, and currently beginning a career in music (though I do plan to go to college and get a "real" job teaching). I've actually been making money for about two years now, and the first response to your query was quite correct. If you want to start, volunteer. It's free advertising for you. Make business cards, and make sure people take some home when they see you play. Play as much as possible and as well as possible, and you'll start getting phone calls. If you can get someone to be your manager, especially if they'll work for free for a while (my mom does the job for me, and she's awful good at it), that's great.