[electromagnetic]

I'd argue that the logic is flawed. Studies have shown that Twitter users in general are more narcissistic than Facebook users (although rather obviously the frequent status updaters on Facebook are more narcissistic than average users) in general.

Given that teenagers are in general the most narcissistic group of all humans - seemingly by biological specialization - that they should be the biggest tweeters.

I believe the reason teens aren't bigger twitterers is because they're not being exposed to it. Online membership is a rather passive recruiting method, it's not like boy scouts where there's someone coming into your classroom trying to get you to join. Teens will have to find twitter largely on their own, which if Twitter isn't advertising to teens it means it largely won't be found until it goes viral in schools like MySpace did in its day, notably another very narcissistic site.

Teens in more affluent areas, with better phones and messaging plans are likely more twitter users simply by virtue of better access.