https://www.nintendo.com/en-ca/store/products/game-builder-g...
The app has tutorials and built in games to get him to work up to making a game.
Surely, his current game is too ambitious for him to pull off but this will get him making something and thinking about programming.
There is also RPG Maker depending on the style of game: https://www.rpgmakerweb.com/products/rpg-maker-mz is the latest, https://www.rpgmakerweb.com/products/rpg-maker-2003 is the oldest and cheapest.