Would you still hire me after 12 years?

Would depend on what those immature mistakes were. If things like poor attendance, erratic work habilts, left withoug notice, those wouldn't affect your eligibilith for hire. If you stole from me, no I wouldn't hire you.

Depends on what you mean by "couple immature mistakes".

I'm well aware of what is typical stuff one has to deal with when hiring teenagers. No, it would not deter me from hiring them twelve years later if they were a basically decent person.

That being said, I've also hired some teenagers that made some really bad decisions that had egregious effects on the workplace and their coworkers. These are decisions that other teenagers were not likely to make and knew were over the line DESPITE their age.

So...were your "couple mistakes" the same types of mistakes that are to be expected from teenagers in general or were your mistakes the egregious kind that really effed stuff up?

You really didn't give us much context.

Not if you made serious mistakes, or left without notice..

After experiencing something similar myself I would definitely be prepared to give you 'a second chance'.

Sure, so long as you didn't steal 12 years ago.

the past is the past , leave it there