Just a few ideas.
If being a firefighter got to him, does he claim any mental health issues? Maybe he can get educational benefits/occupational retraining? Just a thought.
As Cookie mentioned, what benefits can he get? Sometimes the highest paying job right now, doesn't pay off in the end. Pensions are VERY hard to come by the days. I'm sure glad I have mine. I retired at 43 and never had to work again, even though I still do. If he does find something high paying, factor in retirement savings. What people "think" they need to retire and what you actually need are 2 VERY different things. Don't forget about medical. A lot of places have stopped that as a retirement benefit. Medical will bankrupt even the richest of us, especially as we get older.
Education. "IF" he knows or decides, then pursue a degree. If he's undecided, do general education now at a junior college. Don't waste time or money at a private college like PIMA, ITT, ect... the will be overpriced, not accredited (even though they say they are), 4 year schools are overpriced and don't have as flexible of schedules. Doing 2-3 years at a JC and then transferring...you still get your degree from "University of" whatever.
Trade schools. Be careful. These can be WAY overpriced and not worth anything. Again, not all are accredited like they say.
Look 5-10 years in the future. Mechanics must be computer savvy. What about drone/UAV mechanic or pilot? Big futures in that. I see automotive as too volatile right now. We have no idea where that is going.
Lastly, it's not crazy but...what about going to places that interest him and request a "reverse interview"? You go to them and see what opportunities and future they have. You might find that something great now, has a 5-10 year shelf life and then now older...maybe with a family...he'll be looking for a new career. I never saw myself working in logistics, but our company has grow so much and there is no end in sight.