Does Getting Older Always Mean Getting Weaker?
If you don’t exercise and want to start it's helpful to begin by building strength before starting aerobic exercise. Many older exercisers can walk faster and with less risk of falling after doing strength training exercises for several weeks. This is most likely due to stronger legs muscles and better reflexes.
Learn More:
Many Seniors Lose Fitness Due to Lack of Training, Not Just Aging
Personal Training for Seniors
Older Athletes and Performance
Exercise and Osteoarthritis
Older Athletes May Need Custom Exercise Programs
Older Couch Potatoes Gain Most from Exercise


Actually, it does mean a decline in your maximum fitness. However, most people are not at their maximum, so they will be able to improve, for the most part so much that they can be fitter when old than they were before, but not as much as they COULD have been before. Still, do it.
Just don’t mislead them. Aging is damaging.