Research psychologists suggest that  it is time to stop thinking of future health,
weight loss and body image as motivators for exercise. Instead, these experts
recommend a strategy marketers use to sell products: portray physical activity
as a way to enhance current well-being and happiness.

Dr. Segar is among the experts who believe that people will not commit to
exercise if they see its benefits as distant or theoretical.  “It has to be portrayed as a compelling behavior that can benefit us today.”   She said. “People who say they exercise for its benefits to quality of life exercise more over the course of a year than those who say they value exercise for its health benefits.”

The elderly, on the other hand, may get started because of health concerns.
But often what keeps them exercising are the friendships, sense of community
and camaraderie that may otherwise be missing from their lives.

For more information:

http://well.blogs.nytimes.com/2012/08/27/changing-our-tune-on-exercise/