One interesting tidbit I did learn though, when working in Japan it is actually prohibited to discriminate by age and gender. If taken to its logical end then I suppose one merely be shown to be able to do the job or run the business to be allowed to do so.
Yeah, i read somewhere that this is the reason why many schools have more or less limits on students working. And apparently those rules in schools goes very far down in ages, suggesting that kids CAN work if they really want to.
If it was violating any laws...
I think the only issue is that school is mandatory, so they have to be at school when required, outside of that it seems rather open.
Take Makoto Kino from Sailor Moon... lives on own in subtitled anime and manga, though lives with mom in dubbed anime.
There are some ways that can happen for real in many countries, it´s just very very rare.
IIRC, she has an uncle(or some relatives) vouching for her and providing money and being the official legal guardian. But there are ways to get completely emancipated early.
I would have considered it unlikely Haruka or Michiru, in high school themselves, could adopt a child.
Probably Setsuna meddling, one way or another.
Please Twins has the main protagonist as having been a high end computer programmer and he seemed to have been so for some time, despite being in high school.
Has happened for real. In the 90s i recall one time there was a 14(?) year old kid that got hired for programming, was a bit troublesome as it had to be done with the approval of parents, but the guy had worked about 10% constantly up until graduating university. I don´t think there´s all that much (in theory at least) beyond parent/guardian consent stopping anyone here once they´re at least 15, from getting a job. I vaguely recall Japan having SOME kind of limit at age 12-13, but i can´t recall exactly what it was.
Overall, i think all those listed and others are more about breaking the "normal" rather than doing something that can´t be done.