Expanding adolescence?

Many cultural commentators have remarked on the fact that adolescence seems to be lasting into the mid-thirties for many members of our culture. They have also remarked on the fact that children are being marketed to as adolescents: the "tweener" category and the whole scare about girls tarting themselves up frighteningly early, etc. Could it be that these two phenomena are actually to symptoms of the same phenomenon: the flooding of adolescence over its previous 13-18 banks in both directions out to the 8-39 floodplain?

Why should this phase of life be growing so much? I seem to remember adolescence as a more difficult and troubled time than either childhood or adulthood. Maybe it's a phase of life in which people are remarkably susceptible to lame-ass marketing campaigns, so it's in the interest of the advertising industry to prolong this vulnerable phase as long as possible.