Twitter adoption among Internet users more than doubled between November 2010 and February 2012. Now more that 20 percent of all people in the US who use the Internet also Tweet or at least roam the Twitterverse. Additionally, 8 percent of all US Internet users are active on Twitter every day.
Here’s the full article. Who Uses Twitter Anyway? | PandoDaily.
Twitter hasn’t taken off among people over 55, but that is only a matter of time.