I am interested in the statistics of early college graduation, or more generally, the statistics of extreme ages in academic settings (highschool, college, grad school, etc.). For instance, how many students who earn a college degree graduate one, two, three, or more years earlier than the typical age of 22 or so? I am willing for any statistics to qualified in any way (percentages in country W, at university X, in state Y, or from year Z). A quick Google search does not easily reveal this information.
I estimate that less than 5% of the population graduates college two years earlier than normal based on my acquaintances, but this is likely biased as I am a graduate student and it may be smaller.
EDIT: It occurs to me that my question does not ask for any opinions on whether early graduation is good, neutral, or bad. Perhaps it would be interesting to expand the question and have those who experienced graduating early give their stories or opinions.