Teenagers as a group are not trendsetters for other age groups, for example when did you ever see a Justin Bieber hairdo on anyone over the age of 17?

They are time rich and money poor, a situation that reverses as you get older. They live geographically close to most of their friends. This is mostly not true for adults, who tend to be time poor, wealthier than teenagers, and geographically separated from their friends. Because of this, looking to teenagers to understand what most people want from their social media does not seem like a particularly good idea to me.