In my case, I'm a LOT more fit than I was in my 30's. This year, for instance, I participated in my 5th Bicycle Tour of Colorado (450 miles with about 35,000 feet of climbing and high elevations), and completed the infamous Markleeville Death Ride (125 miles, and 16,000 feet of climbing in one day).
In my 30's, I was an overweight smoker trapped in a crappy marriage. Now, at 53, I weigh what I did in high school and can do 100 miles of hills any day of the week. And since the crappy marriage ended, my sex life has improved 1000%.