Contrary to popular belief this post on Mashable highlights how according to a Nielsen report that was compiled from a panel of 250,000 internet users, only 16% of twitter users lie in the age range of 2 to 24. The majority of twitter users (64%) lie between the age group of 25 to 54 and 20% lie between 55 and over. This information is useful for marketers that are trying to reach the teen demographic. Here's the chart that was provided by Nielsen.