One of the things I have noticed that has meant so much to me is finding myself less concerned by what other people think. High school (middle school...) makes us believe that all we know and will ever be is encapsulated in a few short years. We spend way too much time caring about what other kids say about us (when they don't know anything—at least not any more than we do). I have a better sense of self now. I know that if I've worked hard, I've done a good job and no one needs to tell me (though it's always nice to hear it). I also know that I make mistakes, but can forgive myself more easily and laugh at myself more easily. It's not always a perfect system for me: sometimes there are things I know I care about more than the time they are worth worrying about, but it's so much easier now.
Of course, the problems and worries we face when we are older become more serious: fear of losing a job, worrying about the health of children and parents, losing friends to illness or accidents, etc. These are things that happen to young people, too, but the frequency increases as we get older. We worry more about things we didn't have to when we were younger: like politics and taxes.
However, with maturity comes a certain peace, if you're lucky. Maybe it is something we have to spend time working on...consciously. I am more apt to stop and help a stranger (hold a door, carry something to someone's car); I love to compliment people if I feel honest about doing it. (Drives my daughter crazy because she says it's embarrassing, but that's her age.) I know how nice it is to hear nice things from others, so I pass it on. And there is a sense of giving back. When you're more comfortable financially, mentally and emotionally, it's easier (if you're lucky...) to appreciate all that you have and to give back to those who are less fortunate. And I've found it has nothing to do with making me feel important. If someone feels good because I've been able to help in some way, I feel like I've been given a gift. Now it still bothers me if I try to be nice and someone blows me off; I'm still human. Having to look in the mirror is not as easy: those little lines and extra pounds can be a bother, BUT I SEE MYSELF AS A KID AT HEART, and it's easier to age more gracefully that way. Years do not an old person make: some young people are old their entire life.
But many things become less worrisome as we "grow up." And there should be some good that comes with no longer being 25!