Surely you mean "Minimum age", so kids won't see the word "crap" on the screen, say it aloud to their parents, and get the polyester pants sued off us due to public outcry. If, though, you mean "default" as in "Age in which the slider on the profile is set", then I would first say that that is a silly thing to ask about, and secondly, I would say that the average age here is about...ooh... 17/19.
Then again, there is a STRETCH of a chance that you mean default age as in "time spent on the Wiki", which would be good, if it was meant exculsively for Wiki posters like myself, but ten years makes it seem like a ruling-out.
Do you mean "time you intend to be on the forum"? If so, that means that you obviously have a lot of insight as to how long H*R will last, and although I respect your view on the staying power of H*R, isn't that a wee bit too much planning ahead?
Is it one of the above? Or is it something else? My money's on the first suggestion, but could you please shed a little more light on the subject?