So wtf is up with Henry/001/Vecna's age now?

Okay so I was watching season 5 volume 1 when it came out and saw the cave scene so I researched it more and found out that it's something that's a big plot point in the first shadow stage play which I hadn't even heard of before but then when I looked up what the deal with that was and found out more about its story it left me extremely confused along with another scene that was in volume 1. So as we all know in season 4 we see little Henry who's like in the 8 to 10 range (I'm not very good at guessing kids ages just from the look of them and I don't remember if they stated his age at all during that season) and he's this emotionless psychopath that kills his family gets taken by Brenner and then gets turned into 001 and eventually banished to dimension X where he becomes vecna. But then all of a sudden in the stage play and in season 5 he was apparently a normal kid and whatever happened to him happened at some point during High School when he was much older than he was in season 4 which has left me so confused because it opens up so many plot holes. Before when he was just a straight-up villain it made sense but now that they're trying to make him a sympathetic villain (which I don't mind in concept) it's kind of messed up the continuity. Either we're supposed to believe that the kid we see in season 4 was actually in his late teens or for whatever reason brenner let him out and let him live a normal life while also periodically coming back to the lab for experiments which I genuinely can't see happening. I haven't seen the stage play (aside from a few story details) and I know they'll probably reveal the full backstory in volume 2 (which kind of makes the whole stage play very redundant and spoilery in retrospect) but does anybody have an explanation for how his backstory is supposed to make sense?