I've used many engines and shipped many games, including commercial titles (I don't derive a salary from the game industry, though). I think I'd recommend something like GameMaker. I've never used it myself, but it's a self contained IDE that has everything to make decent 2D games. I'd advise against the pitfall that 3D games lure you into. That includes engines that are 3D with a 2D "mode". There is so much leaky ab…
I used to use GameMaker when I was exactly 9 so I would definitely recommend it. Scratch always seemed like it was not at all made to acheive any sort of playable game but GameMaker has a low barrier to entry but can make real stuff. I would try my best to convince him that he might have to learn to make something scaled down and 2D first, and as others have suggested, talk to him about his bigger vision game and bra…
In the beginning all I did was fool around with the example games and tutorials, and that got me started well. Like taking a bouncy ball game, changing sprites, playing around with changing things in the existing logic and every now and then accidentally stumbling upon an interesting mechanic.
The drag and drop interface is really nice for starting out; eventually I got into the scripting part and found out that I had kinda learned “coding” along the way