Throughout life, our nutrient requirements change as our body changes. As we get older, muscle mass and stomach acid levels, for example, naturally decline. You can support your body by providing the nutrients it requires and by adding in some exercise. Don't worry, there's no need to run a marathon, just don't stop moving.
They say that "you cannot outrun a bad diet". Does that mean that there's no need to exercise when you want to lose weight? Not really. While exercise might not contribute as much to weight loss as is commonly thought, there is still a very good reason to keep working out: your body composition. Building muscle has a number of advantages, and exercise also helps to maintain bone health.