Ideally, instead of you deciding for him, try & ask him what he'd like to do. Seems like he enjoys drawing & painting. So if that's what he's more keen on doing, then let him pursue that. If he says he enjoys being on the computer, then let him. If there are other interests like writing or music or electronics or photography, encourage him to follow them.
If you are worried about picking an activity that will eventually help with career prospects, then realize that he's only 12 & there's still some time to go. At this point in time, he only needs to realize that many options are still open to him. From that point of view, it might even be better to expose him to a range of activities that might interest him, rather than limiting to only one such as computers.
Since your question is specific, I'm going to assume you've already considered all that I've said above, & are here only because you want a specific answer. (Disclaimer: I'm not a software-coding-literate person, so my suggestions might very well be off the mark. But I'm posting anyway in the hope that you get a few ideas).
So imo, you could get him started on building basic websites with html. Since he's already built a wordpress blog, you could ask him if he'd be interested in building a website from scratch, i.e. as if a thing such as wordpress never existed. I suggest this route because building a website is one of the few computer based activities that provide almost instant feedback/gratification. (You can punch in a few lines & immediately see what the effect is).
You could ask him if he'd like to build a simple game for mobile or pc & get him started. Now, gaming involves coding as well as creating graphical elements. If he wants to learn the former, you could start with whatever the simplest language is. If it's the latter, you could get him started on building models within software such as 3ds max or maya, & then import them into game engines such as unity or unreal.
If he's interested in knowing how newspaper print ads are created, you could get him started in photoshop.
If he would like to learn how movie effects are created, he could get started with the relevant vfx software.
If he's interested in how djs re-mix music & how music recording, dubbing etc. works, get him started on the relevant software.
If he's more keen on building things & electronics, I'm sure there's tons of simple diy projects that he could do, with (such as Arduino) or without the use of computer programming.
In short, there are quite a few activities that involve computers. It's best to find one that matches his current interests, & one that possibly gives immediate feedback.
HTH.