http://istrategylabs.com/2014/01/3-million-teens-leave-facebook-in-3-years-t...
True, people have different motivations (!) for using Wikipedia and FB. But if other sites are strongly impacted by changing patterns in use by different age groups, maybe it's worth investigating whether something similar is happening to Wikimedia sites, too? Do we have data on page views/user activity by age group?
Cheers, Andrew