Superair pretty much nailed it.
We used to hire most of our apprentices from the kids that came in as interns during their school work-week. We'd pick the kids that were smart or showed promise or sometimes just the ones that seemed a best fit personality wise for the shop. No such thing as MMI back then, it was AMI and we'd laugh at those guys.
I got in as an apprentice by knocking on doors but I think luck played a huge part in it. If I was you, I'd go offer to work at a shop for free for a couple weeks. Do anything they ask, sweep floors, drive the parts truck, deliver bikes, wash bikes, get coffee, assist the techs, anything they ask and don't complain. Never complain. Stay as late as the last guy and offer to stay later. Don't be late for work, be waiting when they get there. Don't expect to turn a wrench or a screwdriver on any bikes for those two weeks. If they go out for beers after work, go with them if they ask you along. Don't act or pretend like you know anything because you don't, at least not compared to a real mechanic, not yet anyway and nobody likes a know it all. Demonstrate your interest and willingness to work hard and don't be afraid to get dirty.
I worked on bikes for nearly 20 years then switched careers and now I'm back working on my bike as a hobby. It's much more fun that way. I'll tell you what though, I wouldn't trade those twenty years for anything. If you're in a good shop with a good bunch of guys, it's a great job. Very fun and rewarding but you won't get rich, that's for sure.