At my dojo, it takes anywhere from 4-6 years. I don't understand this, as I was actually given a stripe early, then told I wasn't going to grade for orange belt after all, since I had not put in the minimum requirement of 3 months per higher kyu. What I don't get is that if you have to put in a minimum amount of time, why is it 4-6? Why does it vary? Could it be that as you get closer to black belt, they start looking at your ability more, and judge you based on that? One can only hope, I guess...