It will take you a few years. It's not like when most of us older guys started.
Now permits and regulations are plenty.. In Michigan, for example, working on other peoples' cars without a license or certification can earn you a super big fine and/or some gray bar hotel time.
I have been a "professional" witness on several cases.
Don't want to discourage you ,but look into all aspects of going into business and stay determined. It takes that and CASH!