Hmm....I now have that song "Mammas, don't let your babies grow up to be cowboys." running through my head.
My father, as a hobby, works on cars. And i use the "works" loosely, as he hires many others to work on the old autos he purchases and then coordinates the projects. We'll get our hands greasy from time to time, but mainly other mechanics and machinist do the bulk of the lifting. From what I've seen being an auto mechanic isn't the best of jobs concerning pay, or with the work done. All to often auto mechanics can be a pretty seedy crowd to be around. From what I've seen, alcohol, drugs, porn, even gangs can be a problem with this group.
But with that said, I know of a few auto mechanics in town that own their own shops, have reliable reputations, and so do decently well as far as I can tell. I guess like most things, if he wants to be a mechanic aim high - be reliable, do quality work, and be your own boss. It could pay off in pay and also in job enjoyment.