She was restricted from registering because the medical forms were required and if I didn’t sign them, she couldn’t have attended. She also could not have used the medical facility if I didn’t sign a form allowing her, at 17, to receive medical services. An 18 year old (at least in Florida) has the right to her own medical records, so an 18 year old could have registered and requested any medical services she wanted.
I don’t know if there were things my daughter couldn’t have done even with a form signed by me. I think she could not have driven a school vehicle, even a golf cart. There may have been jobs she couldn’t have as her school has a lot of government contracts and some of them required the student workers to be at least 18 and a citizen - the citizen requirement was called into question a lot more than the age requirement.
The town I grew up in had a curfew for those under 18. It also had a university and students had to comply. No, not a school rule but a law that affected those under 18. I remember a guy in my dorm was furious that he’d been off campus and was picked up for breaking curfew. He was 18 but didn’t have an ID with him and he couldn’t reach any of his roommates to bring him an ID because they were all out at the bars.