Many 40 year olds manage their lives as teenagers (look at the low birth rate in western Europe, or high divorce rate in the US) and vice versa - teenagers build $15b (if you believe it ;)) companies.
Anecdotal, yes. But your comment relies on a stereotype. How do we know that teenage mothers do not quickly start maturing from the point they become teenage mothers, relative to their peers? They almost have no choice.
(I say that knowing of some concrete counter-examples to what I just argued. But that's just anecdotes, too.)
http://en.wikipedia.org/wiki/Teenage_pregnancy#Impact_on_the...
(I'm not judging this, btw, it's a valid choice.)
In Scandinavia birth rates are relatively higher - definitely not because Scandinavians don't like cars or vacations, but rather because the society makes it easier to have children and a job at the same time (e.g. kindergartens available and so on).
However, it IS fair to say that society reacts to people of certain ages as if the sheer fact of getting older meant instant change in mood and personality. And that's harmful.
All the while, people are getting fatter and fatter, and less and less active. Our great grandparents had to struggle and suffer just to survive. Most of us have never dealt with true scarcity in our lives.
Each generation is getting lazier, more privilaged and more destructive.
Granted, these are just vehicles to maturity, not a promise of success. Everyone fails in some measure, some horribly.
Yeah. They bring out the ASS in some parents.