Exercise is the key. A study of more than 21,000 men showed that fitness, not leanness, is the secret to longevity. If you are fit and fat, you will still live longer and happier with more energy and less chance of disease. First, exercise your heart through aerobic exercises like brisk walking, jogging, bicycling or swimming. Second, build back your muscle by lifting weights.
Repetitions build endurance and increased resistance builds muscle mass.
If you can only do one type of exercise, go the aerobic route. Aerobic exercise increases energy, causes fat loss, strengthens your heart and makes you feel younger. Avoid repetitive pounding and punching motions. These can cause injury. Don't try to prove anything.