This afternoon, Nielsen researchers David Martin and Sue MacDonald posted the Nielsen NetView Audience metric for Twitter in 2009, which shows that the majority of Twitter users are in the 25-54 age group.

The graph would otherwise be uninteresting were it not for the fact that 15-year old Morgan Stanley intern Matthew Robson declared that teenagers do not use Twitter, in a non-statistical representation of Teenager media consumption released last month.

"Teenagers do not use Twitter," Robson wrote. "Most have signed up to the service, but then just leave it as they release that they are not going to update it (mostly because texting twitter uses up credit, and they would rather text friends with that credit). In addition, they realize that no one is viewing their profile, so their 'tweets' are pointless."

Nielsen's data backs up Robson's assertion by showing that even as Twitter's audience grows beyond 20 million, only 16% of all users are under 25 years of age.

The metric only observes Twitter's main page, and not software-based Twitter interfaces for mobile phones and the like. Martin and MacDonald, however say, "It would be a big stretch to assume that the gap in the youth demographic is being made up via other clients and platforms. For example, more than 90 percent of popular Twitter client Tweetdeck's audience is over 25.

"Furthermore," the authors continue, "Twitter.com's reach is 6.6 percent for kids, teens and young adults, whereas it is 12.1 percent for those over 25; implying that adults are trying Twitter at nearly double the rate."