Character growth, you know, like in anime(lol). He is becoming desensitized and is changing, so it is good to show it in his appearance. Satoshi is just a name, although considering ntrman's cinematic univerce(tm) being a thing, it is possible for him to not want to make two different characters with same name. Still it could be just a bait, so people can talk about it while he is not releasing.
What do you mean "real age"? He is 22 years old, swear on me mom's tits. But jokes aside it still would be a bizarre transformation for cucked kid. Rapidly becoming 190cm tall with massive peepee in 3 years is not something I can imagine. Ntr powers i s'pose.