People love to use the phrase, "we're all adults now." I disagree. We're totally not adults now. We're basically still children. In fact, the more I learn about adults (anyone five years older than me, I still have a high schooler's mentality of what constitutes "older") the more I'm skeptical that anyone evolves past the child stage.
If you're a shitty seventeen year old, and then a slightly better but still shitty twenty four year old, there's a good chance you'll just be an almost not as shitty forty year old.
What changes, I think, is the amount of people who can or want to feel responsible for you as you get older. If you're a real drag to be around when you're old, you'll just find yourself in pothole after pothole, with less people to lean on as the years pass.
This is a working theory.