Admittedly, I'm not yet as old as I could be. I don't yet have to worry about aching bones and strange sleeping schedules, but gray hair is already a significant part of my life. My metabolism and energy levels are pale imitations of what they were in my 20s, as are my sense of adventure and opportunities to meet new people.
Your world starts shrinking when you graduate from college, right around the same time your waistline starts expanding. I stopped being anything vaguely resembling "cool" a long time ago, a fact that the use of the word "cool" no doubt confirms.
Technically, rewinding the clock would give all that back to me. I'd be skinnier again, with bright eyes and smaller shirts, and when I looked in the mirror I'd only see dark hair. I wouldn't have to worry about my blood pressure, cholesterol levels, or squeezing some extra exercise into the day. I wouldn't feel time looming over my head, reminding me every day that there's less and less of it left to accomplish the things I want to do. The world would be awash in a sea of possibilities.
I would also be clueless about what to do with any of them. I knew exactly nothing when I was 20, either about myself or what life was really like. I didn't appreciate my smaller waistline or my hopeful young face, always comparing it to the girls around me who were skinny and pretty and everything I thought I wanted to be. I had boundless energy, but not the slightest idea of what I really wanted to do with it. I was scared of things that I later learned didn't matter at all. I made myself bleed wanting things that I later realized I didn't really need.
There is nothing in the world that would tempt me to trade the mind I have now for the one I had when I was 20. The years I lived between then and now were full of irreplaceable lessons, experiences and insights that ended up changing my view of the world. They reshaped me into a smarter, happier person, more at peace with myself than I ever imagined I could be when I was younger. All of those lessons only came because I was in the right place at the right time to understand what was being taught. All of those lessons built on each other, reshaping me as they went.
Even if I could go back in time and tell 20-year-old me everything I've learned since then, I suspect she wouldn't believe any of it. Even if she did, she wouldn't have known how to use any of it. Only time, and living, can teach you things like that.
So, even if someone could turn back the clock, I'd have to pass on that particular miracle. It took long enough to get where I am today – the last thing I'd want is to have to do it all over again.