Look, for the people who enjoy this, good on you. I'm not here to shame anyone, but this is 100% kind of gross. His body may be that of a grade schooler, but his mind isn't. That is a huuuuuge red flag. This dude is out here trying to "undo the past mistakes" which is tantamount to grooming this young girl so that she will like him this time. That is taking away her agency and ability to grow on her terms, and replaces it with the version of her he wants
"But she's so happy," I can hear people say. Yes, but she doesn't know what could have been, and he does. She doesn't get to make the choice to do things different. She is different because he wants her to be. He is basically treating this whole situation as if he is reloading a save file of a dating sim, but with real people instead.