Send him up for a familiarization flight at a local airport and see what he thinks. If you are going to start having him train now, I recommend AGAINST getting anything more than private pilot before going to college because that's generally as far as you can already have and be part of the 141 training program. Send him to WMU, MTSU, or another college that has a robust flight training program to get his ratings. Going to one of these collegiate programs also gives him the chance of getting into the Delta propel program, which at least appears to be a big leg up on career progression.

Delta cares about where you went to school (not necessarily that it was an aviation school just that it was respectable), what degree you got (not basket weaving equivalent, although it's viewed in context of which school as well), and what kind of flight training you received. Not all majors care to that extent, but it can have an impact later in his career.

Start out by sending him up for an introductory flight or two. He can at least get a taste of it and make sure it's what he wants and you can decide how far to go with training beforehand. Do keep in mind that if he does initial training part 61 like that he might have to relearn things if they are not taught in the flight school's methods so it could make it more difficult if he goes the collegiate aviation route.