When Did This Happen?

Okay, I'm admitting it, though I don't know when it happened! I'm not a teenager anymore. I've known for a while in my head, but my body realized it full force on Saturday night.
See, I went to a concert (which was awesome by the way), but it was one of those events where you couldn't pre-buy tickets. So we got there at like 4 pm. The doors didn't open until 5. Once we got inside we sat for a bit, but after the concert started at around 5:45, I didn't really sit for a substantial period of time until we got into the car after 10. So pretty much I stood (and swayed and clapped my hands and screamed and put my hands in the air), for 6 hours straight!
When I was a teen, this didn't phase me one bit, but I was awakened at three in the morning by something that I'd never before experienced post-concert - A LEG CRAMP!
I'll tell you this, it was no fun. So I'm sitting there in my bed, trying to get rid of the cramp, and I'm wondering, "When did this happen?" I'm young. Cramps don't happen to young people.
WRONG! I'm not old, but the twenties are definitely different than the teens, or maybe I was just better at ignoring things when I was a teen. No, that couldn't be it, this cramp was much too painful to be ignored.
Whatever it is, I'm thinking that I'd rather go back than forward. But seeing how that isn't possible, I guess I'll just try to find the humor in it! And hopefully I won't need a cane by the time I'm thirty!!