Or buy him a MiYoo/Ambernic and add Pico-8 games. Pico-8 is a great platform, games are free and short and sweet. In addition, you can pry under the hood and read the code, modify it freely, etc. It's a perfect on-ramp for programming.

I personally got a Miyoo for my kid but ended up getting one for myself. The fun and nostalgia are there.