He should finish High School. There is no rush in 1 more year he will have plenty of time to be an adult for the rest of his life. I think he should carry on and maybe take some classes at Community College like Accounting, etc. Doesn't have to get a degree that's just a piece of paper.

Ultimately, in order to run a business it's no longer about working on trucks which I know many on here get that. What you don't want is him working for "The Man" the rest of his life. If my kids want to dig a ditch that's fine they just aren't digging it for someone else @ $10/hr.