Both my lads had 50cc mopeds and geared bike, taught them about riding on the road and riding in traffic, the eldest went on to a 125 and them passed his test, he’s just sold his Husquvarna 300.
They both learned to ride off road, where they could be as reckless as they liked, I think that helped with their approach on the road. They weren’t racing about taking risks (or at least from what I saw)
Personal opinion is that it made both of them a better car driver, passing their tests first time and also alot more aware of cyclists and motor bikes.
The big question is would you rather him on a moped or a push bike?
I rode bikes from an early age and had a 125 at 17, didn’t want a moped or a 50 though. Riden and raced bikes all my life, lost some good friends on and off the track.
Tough decision, only you can make.