In my style/school it will take anywhere between 3.75 years or longer. For example it will take the following time in months to each kyu rank :10th gold 3-4 (its not given its earned), 9th orange 3-6, 8th purple 1st 3-5mos,7th purple 2nd 3-5, 6th green 3-5,5th 3-5 4th 3-6, 3rd brown - 1st brown 12, sho dan 6-12. Most would say that a black belt is no big deal, as you now know the basics. Its just the start!!! How much of an expert are you after four years of high school or college. Train hard and have fun.