Also is codified by law specially on the entertainment industry where they snatch girls from 15 to up but tldr and im vague remembering here Haachama required permits from her parents and her school to be a member of Hololive, later i was notified that this is absolutely normal and we westerners were weirdos for complaining about it
It's "normal" just about everywhere. Professional tennis careers pretty much always start in the mid teens, for example (Federer did his debut at 17, Graf at 13 (!)), nevermind female gymnasts. Britney Spears was signed at 16. Natalie Portman got her first co starring role at age 12 (playing a twelve year old girl hitting on a professional killer and trying to convince him to take her virginity, no less).
Honestly, in theory, I see nothing particularly wrong with streaming in one's mid teens (well, not beyond "What are they even going to talk about with a life experience of zero?" No Marines, Luis or Chocos here). People take part time jobs at that age, too, and the average 1- or 2view won't have a larger audience than when participating in her school's theater club, either.
But these part time jobs do tend to be rather less sexualised than most vtubing, and it's basically guaranteed that the audience of a mid teens female streamer would be watching for prurient purposes.
So in practice, eh... getting me to sign that permission slip would be rather difficult.
It's not an accident that the kinds of streamers whose content I'd be fine with hypothetical offspring of mine being inspired by (e.g. AZKi, Lui, Clio) are all 30+.