This is an interesting discussion. In MN, juniors and seniors can take college classes for college and high school credit. Several of us on the team do this, and some of the mentors and other members joke that we ought to register as mentors because we're not "pre-college age" if we do this.
The catch is that we're still technically enrolled at our high school, just not for any classes (except for those of us that only do this part-time).