Youth is a time in life when we look great, we have energy to spare and we spend inordinate amounts of time trying to attract a mate. Because that is what youth is for. It is for starting life, finding someone to spend it with, and in many cases, someone to have children with. Or, if you are not like me and marriage or children were not something you wanted, youth was a time for getting set up in life, starting a long-term career, finding yourself and your interests.
Which leads to now. If you were successful, you've got those things. You've had a mate, children, a career started etc. If you haven't got those things, this is a time in life where we begin to reassess and strive to find those things we now know, with time and experience, will truly bring us happiness.
What I have overlooked is the amazing success I've achieved. I have a marvelous husband and wonderful children. I have figured myself out enough to know I love geeky things, electronics and writing. And the most fulfilling part is that I get to pursue those things. So, if I'm a little heavier than I was before, if I have a few wrinkles, does it in the end define me? No. In fact, why waste my time wishing for my youth back when my youth brought me the things I wanted? I should be enjoying those things now that I have them.