Here’s an interesting bit from Jakob Nielsen’s Alertbox on Teenage Usability:

Teens are not technowizards who surf the web with abandon. And they don’t like sites laden with glitzy, blinking graphics. Teens are often stereotyped as only wanting things that are bold and different. They’re also often viewed as being fearless about technology and constantly connected to some form of media. Although this might be partially true, it’s an oversimplification and letting this steer your design can lead to disastrous outcomes.

Some of the research findings may go against commonly held beliefs, but they should be taken into account when designing web sites for the teen and young adult demographics.