It is not news. NYTimes just published an article Who’s Driving Twitter’s Popularity? Not Teens.

http://www.nytimes.com/2009/08/26/technology/internet/26twitter.html?_r=1

some interesting points

“Though Twitter’s founders originally conceived of the site as a way to stay in touch with acquaintances, it turns out that it is better for broadcasting ideas or questions and answers to the outside world or for marketing a product.”

“The public nature of Twitter is particularly sensitive for the under-18 set, whether because they want to hide what they are doing from their parents.”

Let me add another figure of twitter demographics from comscore shared by cambodia4kidsorg on flickr.