At first my dad put me a bit on CodeAcademy [0] which taught me tons of basics but didn't really get me hooked.
What really got me into coding was by thinking of a way I could use it to build something related to my interests or that would be useful for me.
That seems to be what you're doing with the games by linking it to something he's interested in so that's nice.
It can really be anything though, and you should try to show him the enormous area of things he can do with coding.
In my case I wanted to do my english homework faster, so I tried building a very simplistic program that could find literary devices (metaphors, similes, alliteration) etc... in the literature texts I had to study.
Also you should make sure you don't force it and that the passion and interest comes from him, which seems to be the case with the way he asked for books about coding.