You might want to check state law. Things are changing fast. Here, it used to be you had to have three HS science classes before being eligible for college courses. Now, due to a change in state law, with an adequate SAT/ACT score, they actually can't prevent someone from taking college courses.
It's tiring to live in flux, but some of this is real improvement for us.
My experience is the opposite. In my district the rules are becoming MORE strict than than they used to. It used to only be one or two profoundly gifted students and the district was flexible. But it is becoming very popular for some families to push students pushed ahead who aren't really read for it and the district has clamped down. I've never seen a student skipped a grade in my district, the only case I heard of was a student who went to private school until 3rd grade.
In our district you get no CREDIT towards High School graduation from any class taken prior to the fall enrollment your freshman year, except those the district offers. (very limited summer school offerings) This includes college classes. Community colleges do accept students as young as 12 but that's most commonly home schooled kids. My local community collage requires approval from the student's school for enrollment if they are under 18 and don't have a H.S. diploma.
