How do you become a mechanic?

Your local quick lube will hire you without any experience. This is a great place to get started and to see if it’s for you ! Then, you could get some schooling , etc if you wanted to head in a more mechanical direction.

I'm no where near qualified to specifically answer this as I'm only a level 4 grease monkey and not a full fledged mechanic/technician. However, my brother is a mechanical engineer (and his story might help) and both of us have gone through a whole slew of cars and own classic autos with which we enjoy. We weld, wrench, paint, and have done everything from an oil change to swapping out engines that were not created for the cars we shoved them in...

We learned the hard way - experience is a great (painful) teacher. 

You have a huge leg up, the internet and forums galore to learn all the ins and outs without having to make some of the mistakes we made. With that said - if you have your heart on wrenching as a profession - I would recommend some of the paths my brother almost went down before switching to study mechanical engineering.

1) Trade schools - here in the south east there are several established, reputable trade schools. One of which is tied directly to NASCAR and others to various dealerships across the region.

2) Community College - not as specific as the trade school, but there are heaps of ancillary courses you could take that include more than just knowing the ins and outs of car from understanding business accounting to body shop and welding, etc.. Granted some trade schools will cover rebuilding an engine, camshaft design, and transmissions beyond what the community colleges can offer, but you gain a more rounded knowledge portfolio.

3) Apprentice - this one is a toughie. We didn't have a local restorer nor a dealership willing to have a young kids try and help out. This method is the most direct but it leaves you vulnerable to distress when change occurs at the shop. Should you wish to go else where the experience you gain will be invaluable but other shops might have difficulty quantifying that worth. 

4) BS in ME - after a long period of wrestling between these options, my brother opted to forgo Trade School and went with getting his Bachelor's in Mechanical Engineering. His final choice boiled down to selecting what would offer him the most secure option with the widest amount of choices and that was the degree. It didn't land him his dream job but he is able to play with his dream cars. 

Take care and reach out if you have further questions about cars!