Ross Mayfield posted a graph on his site showing the age distribution of LiveJournal users (via LiveJournal Stats). That inspired me to look at the data for the ageless project. Though the sampling is obviously much smaller (ageless has less than 1,400 member sites), it's interesting how the age distribution differs. It appears the typical LiveJournal blogger is considerably younger than the typical 'ageless' blogger (not all ageless sites are blogs, though most of them are).
This seems to be an opt-in poll, but results vary significantly from LiveJournal's demographics. Be sure and read Jeff Jarvis' comment (he rightly points out my headline was a hasty generalization) and Marc Canter's point that community is not a commodity.