Which still doesnt make a lot of sense since he was also a Teen Titan back when he was 10. And then tried to put Jon on the team in Percy's run.
There really wasnt much of a point in aging him up. But since he's more or less the same anyway I dont think there's much of a point in taking him back to 10 either. Just keep him where he's at and hopefully he hits puberty in the next time skip xD
(Though I've always kinda suspected the reason he hasn't grown much is because of the time he'd spent dead. That was like a year right? So he's technically 13 but could physically still be 12)