My school has something like that too, called "pooms." I think it should be based on maturity-not cold, hard ages facts in stone. I've been frustrated countless times because of age restrictions (not only for rank). For example, I'm exteremely young for my rank and I know I personally understand more of the spiritual/mental elements of my art than many-most?-people in my school older than me. But it's interesting. TKD is demanding and most (as there are exceptions) younger people's bodies/minds just aren't developed and, you know, there yet. Anyway, I think it all depends on the individual student. The problem with not enforcing rules is that some not-so-nice dojangs will start awarding black belts left and right. But after all I've said about age restrictions being relative to the student, I really WOULD like to see less of those really little black belts. It's simply not fair to the people-regardless of age-who really and truly deserve it. Black Belt measures time and experience too.