Check out this fascinating NPR study about the factors that cause stress and the distribution of stress across age and income brackets.
The two things that stood out most to me:
--Young people have a LOT of friend drama compared to the older age brackets. Apparently when you hit 30 you either become very mature, or you just don't have any friends anymore.
--Dissatisfaction with how one looks appears to be related to some kind of mid-life crisis--the younger and older age brackets experienced less stress related to their appearance than the middle age brackets did. Dissatisfaction with appearance as a source of stress peaked among 40-49 year olds, which I actually found pretty surprising. (I had assumed the 20-somethings--with their insecurities and their slowing metabolisms--would carry this category.)