First hint of gettiing old (I was about 35 or so) - me and the chick I was hooking up with joined some kids in a pickup football game. The first time I get the ball, I make a sweet juke and headed in for a TD and immediately pull a hamstring.
I never stretched before pickup football with my friends growing up, into my 20s even, but 35+ requires it. More than being embarrassed, I just felt it was so DUMB.