My story is a bit similar to yours (I'm 61 now), and if there's one positive thing about this, it's that with age comes the determination to follow up on what we've put our mind to.
I'm a bit of a gear head in everything (I live in an old house, enjoy classic cars, motorcycles, vintage motorscooters, wrist watches, etc.), meaning, whenI pick something up (started tennis a few years back, and l love it), I tend to go all out and reward myself. That's probably not a good thing, as it costs money, but we all need our stimulants, don't we?
On You Tube, there's a girl with the name "RachelF" and she started learning the guitar 3 years ago, documenting her progress after year 1, year 2, and year 3. She uses exclusively an electric guitar, and loves it.
Your son may be more motivated if he can use an electric guitar as well. In fact, I'd venture to guess that most kids feel that way. If you can afford it, I think you should allow him to get a rather inexpensive electric, such as a Fender Squire, and suggest to do what I do: learn on the acoustic, then repeat the next day on the electric.
Just my 2 cents.
