Users are concentrated in the 15-19 demographic...regardless of how many are over twenty, there's still a higher concentration of users who are 15 to 19. And comparing users over twenty to users under 20 is not a fair comparison because you're comparing an age pool that's out of 20 years to one that half of that (I don't think people who are younger than 9 can realistically function in a forum like this :P)
I guess probability isn't one of your strong suits
