Flight Training at 15?

I started flying lessons at age 16 and finished my private at 17. It took me
the full year. I only flew about one per week and though about it most of
the time. That worked well for me. I took my checkride with just barely 40
hours (and passsed). Spreading out the training may end up requiring more
hours but that doesn't seem like a bad thing to me. If there is enough money
for 60 hours in a year, is it better to get the license in 40 hours in the
first two months and then spread the next 20 over the remaining 10 months. I
would rather spread the 60 more evenly over the full year, even if the
license comes at the end.

I was the first person in my family to take an interest in flying. My
brother and I had each saved up enough for a car by the time we were 16. He
bought a car. I got my private and drove the family car. The money even let
me fly a few hours after my license before it ran out.

I gave up flying for 12 years starting in college. I stopped because I
didn't have enough money. I didn't start again until I felt I had enough
income to sustain it. (My wife doesn't necessarily agree that we have enough
income for flying, but that is a difference of priorities.) Something
similar is likely to happen with your son at some point.