[Cavernio]

I've heard theories that our nutrition is making girls reach puberty faster, something about the amount of fat in our diets. I would certainly believe that being malnourished would hold back puberty, so maybe its just that people aren't malnourished. Also I'm pretty sure most bodily processes can be affected by psychology.
I really don't think media causes people to be immature. Its that people don't have as many responsibilities, which in turn causes people to spend their time doing what some might consider immature things.