I, myself, would love to go back to being 17 and starting my life over from that point. Everybody has regrets, and while some folks like me would jump at the chance to do it all over again (but differently, of course), many, many people have the sentiment "You couldn't pay me enough to go through those years again."
I had a pretty good time in high school, and many of the friends I hang out with decades later are the people I was friends with in high school. But I recognize that my experience is somewhat exceptional.
Now, your twenties - your twenties are pretty awesome, so don't despair. Youth, health and beauty combined with freedom, social/romantic opportunities and relatively few responsibilities. Enjoy the opportunities you have while you can; physical maturity brings its own experiences to savor, but you'll never be young again.