CLEP is great once he’s got a goal and a plan. Right now, throwing new and different ways of him NOT clarifying his educational or professional goals seems to me to be a giant red herring and potential waste of time (opportunity cost, not suggesting that the material in any way is a waste of time.)
There are late bloomers in the world, and then there are people who for complex reasons (mental health, physical health, substance abuse, upbringing/culture, socio-economic limitations) fail to launch or launch at some point but never really get in gear or enjoy what they end up doing.
You sound like a fantastic and supportive parent. Your son is very lucky. Just make sure you guys keep your eye on the ball so he doesn’t end up 40 years old in a dead end job which he hates but has to keep because your financial support ran out 10 years earlier, cursing himself for not having developed a plan in his 20’s.
If he’s getting A’s in calculus, I think you can take a math limitation/dislike off the table as an issue.
So you’re really down to slow processing speed, intense perfectionism, and a dislike of personal/essay type writing as his issues? Has he tried a therapist with expertise in CBT? Seems like if he can get a handle on the perfectionism, he’s going to look more and more like a large percentage of the college bound population!