I'm still thinking on this one. I think that, without Christ, most people adapt to the world. My friends from back in the day, late teens and early 20s...they're well-educated now and have jobs and such, so they're not drinking and smoking reefer all the time, and they're thoroughly middle/upper middle class in outlook. So, yeah...they changed, or at least their behaviors did.
Its good that people grow and change. I think the big difference is between being conformed unto the ways of this world vs transformed by the renewal of your mind. I'm wondering if maybe a lot of "maturity" for those in and of the world is just being somewhat hardened by sin.
Also, economic status changes us, marital status changes us, education changes us, kids change people...on and on it goes.
I tried to think of people from HS while reflecting on this one. I found one former friend...its crazy...her Facebook...she's listening to the same music, reading mostly the same books. Its weird because I think she has a masters now, but...wow. I don't think she's changed a whole lot, obviously.