I agree with Ba Bu. When I first tested for my black belt in TKD back in 1990, I was 17 years old. I tested with several other kids from other schools and clubs in our association. When I watched the video of my testing later that same night, I was shocked and appalled that some of the other students that tested with me were even allowed to test for black belt, much less a red belt, brown belt or even green for that matter. It was very clear to me that they came from "McDojo's" and it definitely didn't give me a good impression of their clubs, instructors, or even my very own association for that matter. I felt if they were going to give these other kids (who worked about 1/4 of the effort that I did) a black belt, it totally "cheapened" the rank of black belt in our association in the eyes of others. The association also allowed an individual to test for black belt at any age.
This had a LOT to do with why I left the association after only a 1-1/2 years of receiving my black belt.
Today, in the system that my wife and I developed and teach, we also have minimum training time at each rank established. But that doesn't necessarily mean the student will be promoted once the minimum amount of time is reached. It depends on whether or not they know their requirements and, more than anything else, can convince me that they can perform them effectively and have a good basic understanding of the mechanics involved.
I also refuse to promote anyone below the age of 16 to black belt. The reason being because I believe a "black belt" should possess the ability to defend themselves against the average adult and should be considered to be among the "best of the best." I personally don't believe your average 10-year old black belt can do that. If I did, I would love to see them fight against an adult who is among the beginner or even intermediate ranks.
We also present a general co-ed self-defense program that will teach you the basic tactics and techniques of our system (white belt to yellow belt) But that's as far as it goes.
Just my two cents for what it's worth. 
Joe Walker – Chief Instructor
RADE TACTICS Modern Combatives & Self-Defense
Hudsonville, MI
http://www.radetactics.com