How long will it take to be a professional auto mechanic?

This all depends how fast you learn. Usually it takes at least two years of turning wrenches at a low wage before you are even ready to be considered a true mechanic. Even then there is a lot to learn. It usually takes about five to ten years before most employers really consider you a professional auto tech. It all depends on you. There are some people that never get good at being a mechanic, and never do well even after a lifetime. There are others that pick it up fast, and become lead techs within five years.