Exercise causes your brain to adapt. This improves brain function, and it doesn’t matter what your age. Researchers have shown children who exercise (games, play etc) have a greater mass of brain matter. This makes them smarter. This becomes more relevant the older you get – exercise will prevent the loss of brain function that is associated with dementia.
The human body never loses the ability to adapt – whatever your age exercise will stimulate your body. Exercise achieves much more than strength adaptations though. It improves proprioception (balance, stability), joint stability, improves range of movement, functional capacity – but exercise is also medicine. It stimulates the body to heal. This research is interesting: