As someone who has never had a real childhood passion for flying/aviation... I would consider having him getting his pvt pilot license and then go from there, don't try to plan too far ahead... I started my flying career at 23 ( im now 25, student pilot ).
IMO, I see people who are passionate about flying since they were 6 years old have a harder time staying in this industry when first starting out. In some people with this passion,their work and personal life is almost mixed together, and when times in the flight industry suck, their whole life sucks and they are miserable. I'm not saying this is a bad thing to have but it can be expected. I have also had conversations with airline hire managers where they are looking for more well rounded people who have a life outside of just loving to fly.
Most people in their life will have 7 career changes ( statistically, but I see more around 3 ). I would make sure he is fully interested in aviation, because having a career change during his training will be a huge economic and emotional expense, esp if he goes the mill route early...then hes really screwed.
I would suggest the military for flight training because of expenses, however you may deal with military budget cuts in the future esp with guard units, thats also another thing to consider.
If you go the civil route, your risking a lot of your income for this adventure... but it pays off in the long term esp with the pilot shortage coming. Big airlines are looking for solutions to find new pilots...Ive heard of airlines thinking of doing 12 year contracts with the company and they pay for your flight training ( that's what they are looking for solutions, doesn't mean its going to be remotely true... but a possibility none the less.
Either way you go just make sure hes committed, that's the biggest challenge I believe. There will be times where he will be tested on it. Its an exciting field to be in. Hope this helps.
PS it doesn't matter what degree he gets, even if its aeronautical...that bs excuse will not suffice once the pilot shortage happens. Job security will be a thing of the past.