Did Charlie X's temptation to use his power keep him from maturing and learning?

Yeah, I think that's what they were getting at with that episode.

a lot of ST TOS episodes seemed to involve God like beings who turned out to have childish qualities at some point, now that I think about it. If had a better memory or were feeling more motivated, I'd list them here.

Certainly his lack of contact with other people kept him from growing, or from being anything other than completely self-centered.