Have you looked into the vocational education programs in your area? Whether it's HVAC, auto mechanics, electrical work, plumbing, the trades are usually in-demand. Give that housing starts are down and have been, the market is way-depressed from the boom days, of course. Same for commercial and industrial starts. But, if you are good at what you do, you can usually find work in an urban environment.
Realistically, I don't think being a specialized motorcycle mechanic is probably going to be as-easy as being a skilled tradesman in one of the disciplines, or a competent auto or truck mechanic. Since Dad is already familiar w/fleet maintenance, he has a good idea of what things are like there as-far as is there work?
I would strongly suggest not investing in a private school technical program as you can probably get an equivalent education at a public institution for far-less. That's what the vo-ed tech centers do best, deliver a good basic education for less.
Being an auto mechanic is better than restricting your operations to motorcycles/personal watercraft/atc's. You need versatility, becoming proficient as an auto technician will provide him with a skill set which can easily transition into bikes w/additional training; meanwhile, the number of jobs available is better for auto techs than bike mechanics.
If he decides he wants to get an A & P license for aviation work, he may have to relocate for the best opportunities or to attend a good school. Patmax's suggestion of Embry-Riddle is a good one, as they are among the best in the country for aviation training and jobs after training for their graduates. One of my friends is a graduate and she (yes, she!) has worked in several of the largest markets for aviation in the country. She went into aviation administration instead of mechanics, but she has made a very good living for herself.
Ultimately, it is his decision, but before he signs a contract with some private educational provider, he needs to examine the public educational options. The other thing to remember is that he will need to be committed to lifelong learning, which is the same thing I inform my EMS paramedic students. That is just what you have to do in the field, and mechanics of whatever types of equipment he chooses as his field is no different. As the technology changes, he must constantly stay-abreast, in-service training will never end until he retires.
It sounds like he is motivated, good for him, with a bit of research and guidance, he can make an informed decision instead of a hasty one which could saddle him with significant debt for a long time to come.