One of the things that I sometimes worry about with younger people I know is if and how quickly they'll be eaten by the world. A quote from the musical 1776 comes to mind - there are two kinds of people in the world, those who have commitment and those who require the commitment of others. Phrased in the terms of strength of personality, this might measure the extent to which people's personality and lifestyle depend on those around them, and this varies quite a bit. While in the parental nest, people are like sponges, developing and taking influences from all over the place - I think one of the difficulties involved in having kids learn to say no to strangers is that tendency - absorbing personality elements and having trust in others are similar traits. As we get older, we gradually narrow how open we are to integration of new characteristics, with each person presumably at a distinctive rate. I was still defining myself throughout university, as most people I knew were - my rate of change only slowed down significantly about a year after I graduated. There are presumably other types of events that can lead one to open up to rapid change - becoming born-again or changing religion/world philosophy, or perhaps moving to a distant, different country. I have a suspicion that people with a weak personality are always open to a lot of this kind of change, and that's what causes them to embrace cultural death in age - a move to the suburbs and embracing its values leads to intellectual stagnation and saps vitality. I think very stubborn people who have firmly decided who they are and have the strength of personality not to adapt to the people around them can progress much as they were in University times, even through a possibly drudge job. There's the issue though that most people won't -- most of the interesting, lively university students will likely lose that spark, partly because many don't know they have it, partly because bracing against that that would take it is not an easy thing to do. It's incredibly easy in academia to be mentally vibrant - it's almost status quo (which is one of the things I love about University environments), and the force of personality/juche involved in staying afloat in the outside world can even be harmful in that environment. In theory, people can fine-tune their acceptance of input to accept only from a few sources, although because this acceptance is partly emotional and subrational, this is not a foolproof tactic.
Of course, all of this comes from my perspective that academic culture is desirable and that suburban culture is one of the worst, least-human cultures humanity has produced. Perhaps some of my readers will disagree.