However the research conducted over the last few years indicates that the real situation is a little different.
Based on the most recent Pew Internet research (of US internet users 18+) the median age of popular social networks are as follows,
- Twitter median user age 31yrs (stable from May 2008),
- Facebook median user age 33yrs (up from 26yrs in May 2008),
- MySpace median user age 26yrs (down from 27yrs in May 2008),
- LinkedIn median user age 39yrs (down from 40yrs in May 2008).
Neilsen data from February also suggests that Twitter is most popularity among older demographics, with adults ages 35-49 having the largest representation on Twitter in February 2009, comprising nearly 42% of the site’s audience.
Pew Internet's profile of a (US) Twitterer also provides useful information on who is Twittering - and why.
Age Distribution of Twitter users (Comscore - April 2009)