but you'd have to progress pretty well/fast; the minimum time would be just under 7 years for Yondan.
If you start when you're fifteen and trained almost every day for the first year then for bring total days up to just over 1315 days over 7 years you could meet minimum requirements by the age of 22...
Minimum requirements; I'd be surprised if this was anywhere near the norm though...
I'm wondering: do you really count the training hours at your dojos? Because in our place (and I think in other I know, too), we don't keep lists or anything, so I honestly couldn't tell you my training hours. We just look at the requirements in years (or months, for the kyu grades), those have to be fulfilled, and then the teacher decides if you're ready or not. If you haven't trained reularly, you probably won't be...