The PDF has 10 pages of specifications.

Section 5 lists the powers-that-be:
"The rules may be modified only by agreement of the superintendent of public instruction, state board of community and technical colleges, the student achievement council, and an organization representing the interest of the public baccalaureate institutions."

Section 15 includes:

Definition 2(b) is very precise in limiting to students with 10th, 11th, 12th grade placement.

Definition 8 limits any potential state-funded subsidies to students with 11th or 12th grade placement.

Section 130 includes:

The college must enroll the student.

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A few thoughts, after having skimmed through the PDF:

One could petition the governing bodies outlined in Section 5, but what would the basis of the petition be?
Usually in advocacy, one presents the student's unmet needs but it seems the school is allowing the child to take the class. The student will receive regular high school credit only, not dual credit granted by the college as well.

If there is another state law which discusses age, such as college matriculation/enrollment age, it may be possible to show that definition 2b is unduly restrictive, and use that to convince the powers-that-be to change the definition listed in Section 15. However it seems unlikely that one would find an inconsistency in age-related policy, which could be used in this manner.

It may still be worth your time to inquire of the powers-that-be as to why the dual credit is limited to 10th, 11th, and 12th grade students. Just inquire, do not attempt to persuade or convince: In other words "float a trial balloon" or "test the waters".

That said, it appears any potential change would come slowly.

Seeking a 10th grade placement, as others have suggested, may be a clever work-around. smile However it appears that a grade-skip must be done proactively, as the PDF describes annual agreements which must be completed between the high school and college institutions. Therefore the two options which I see for his immediate choice may be:
1) Enjoy the course, learn a lot, and accept the high school credit.
2) Drop the course, back-fill his schedule with something else, and take this course next year when he is a sophomore. (What date is the school cut-off for add/drop class schedule changes?)