My mother dropped out at 14 and got a GED by 15 back in the 70s because she was so bored. (Parents didn't believe university was for girls, so that wasn't an option).
Seems like a way to screw over a particular subset of kids.
I dunno about why. But it was set at least in the late 90s. I took the California High School Proficiency Exam back then because it had a lower age requirement (and I was in California).
I just did a web search. I didn't realize they had age requirements. Thank you.