I went to WDW with my DS16, his DF16, my DS13, my next door neighboor, and his DD13. I'm 43 and my next door neighbor is 48. We went to Typhooon Lagoon for the better part of a day...
We all spent a lot of time in the Wave Pool, did lots of slides, etc. My neighbor and I told the kids to meet us at our chairs at 4:00 so we could leave before the crowd tried to leave at closing (5:00). At 3:55, he and I were doing slides and knew the kids wouldn't be ready yet, so we did a few more... we got back to the chairs around 4:30 to find 4 worn-out looking teenagers, huddled together in their towels, saying "Where were you???" Here we were, two 40-something guys, racing back in from having fun on the slides!!
Silly kids, can't keep up with us! You bet, the water parks are great!