When you exercise, time stands still.
Sister Madonna Buder started running at 47 and did her first Iron Man at age 55. Now she's done 45 Iron Mans. She's 86 and going strong, and says she "trains religiously." She's the perfect reminder to get out and enjoy your body.
And if the Iron Nun isn't enough of a kick in the pants for you, there's always 97 year old Charles Eugster, who holds the 200m and 400m sprint world records (for age 95+).
He can do 50 push ups, and took up bodybuilding at 87 so he could impress the girls, according to this BBC video about Charles. What a character! "Aging for me has become an enormous pleasure, a delight, a joy!"