Grandma,
There are a lot of long term health advantages that come with doing regular physical activity. It can help with joint issues, as some pain is linked to stiffness and walking regularly works the joints to make them looser and easier to walk on. It also helps energize you and does well for your heart by lowering the risk of heart disease. Exercising for the standard 30 minutes per day helps you lose weight, improves your cholesterol and can lower your blood pressure by as much as 5-7 points.