Consider the military! The military gives its people some top-notch training. Mechanics is not as easy as it once was. There are different components you will need to learn: engine, transmission, steering/suspension, drive train, exhaust, electrical/electronics, , etc. And of course, the cars now have computers that are supposed to help with the diagnostics, but, it is still important to be well-trained. The need for training will never stop. And there are different certifications you can get.
Outside of the military, there are some good technical training programs, some of which are reasonably priced. Check out the local junior colleges. Get a part-time job at the first available opportunity, such as working at a shop that does tires, or oil changes. And if possible, find an older mechanic who can tell what is wrong with a car just by listening to the engine, and make him/her your mentor!
Best of luck!