At 17, I was doing brake jobs, tune-ups, audio installs, and every other car repair except painting you can think of. I was lucky enough to start in my family's shop when I was 14, turning a lot of wrenches from 16-on.
If you get any kind of chance to get into a good shop at the ground level, I recommend it. Not the best pay if you stay at a small shop, but looking back on things, those were great, great years.