When we think of athletes, we think of kids, college athletes, or professional athletes. But of any group, the health benefits of exercise are most pronounced in the elderly. They have the most to gain. People don't think exercise makes a difference because they're getting older anyway, but just the opposite is true. In fact, the number 1 cause of morbidity in the elderly is falls.
Exercise makes muscles and bones stronger and lessens the likelihood of falling.
Let's say I have a parent at home who's 70. It's never too late. There's exercise for every level for what they want to do. Not everyone can be a ballet dancer like Marianne. The local YMCA often has swimming programs, elder fitness programs, and plenty of things to get involved in.