You're only as young as you feel?

Both Dave and I have been walking around like old folks: moaning and groaning every time we move. (Is this what we have to look forward to?)
While boating, I forgot that I'm not 25 any more, not 35, not even 45!! I decided to water ski. Easy and fun. I used to be fairly good.
Pulling my skis together used a muscle which didn't want to cooperate. This left me limping for the past two weeks now.
That's not all.
When we were bringing in the boat, Dave slipped on the moss on the ramp and crushed his ribs against the trailer.
We gave him a blessing and took him to the emergency room. We needed to make sure he didn't have a broken rib which could puncture his lung. He was in a lot of pain, and has been for these two weeks. Not fun!!
Turns out his ribs are only badly bruised, so that is good.

If you're only as young as you feel, why is it that I feel so young, but my body tells me differently?