Twitter and Status Updating, Fall 2009 | Pew Internet & American Life Project
http://www.pewinternet.org/Reports/2009/17-Twitter-and-Status-Updating-Fall-2009.aspx

Encuesta Pew 2009.

the median age for Facebook is now 33, up from 26 in May 2008

stats for people using twitter facebook among adults

newest numbers. Annes summary: The median age for a Twitter user is 31. MySpace = 26. Facebook = 33. LinkedIn = 39. http://bit.ly/PIPtw (only American users)

Great info on average age of users per channel.