My dad became a mechanic straight out of high school. He worked for the Honda dealership at age 18. He then went to a Ferrarri dealership for 2 years. After that, he had enough capital to open his own shop. He's had great success with it.
If you want to make a good living as a mechanic, perform everything to the highest standard you can. Always use the best parts, refuse to do lower quality service. You want the image of a professional, automotive technician. Not a garage greasemonkey. Get qualified for everything you can. Keep up you ASE certification etc.
My dad cornered the market on European luxury cars in a growing upper class part of Houston, which has now expanded incredibly. By maintaining a professional appearance (both his workers and their uniforms, and the shop's cleanliness), doing the best work possible, and networking, he has been very successful. He does better than any other mechanic I know. He's also worked day in, day out for the last 30 years. His personal life was partly ruined by it. Divorce, isolation from family etc. However, that may not be the route you go.
However, its been hell on his body. Years and years of being on his feet ,leaning over cars, looking up into cars, looking down into cars etc etc. His back and neck are constant sources of pain and there's not much he can do about it. He's got an infinite prescription for vicodin now. He's the Dr. House of the automotive world. "Its not the time, its the mileage" he always says.
Anyway, it can be a good career path, if you're smart and business-savvy.