Make sure your exercise includes aerobic, strength training, and flexibility exercises. Of course that is providing that your doctor says that it is Ok for you to do all these. Aerobic exercise is great for strengthening the heart and lungs, which in the older generations can be the most common sites of terminal organ failure. The stronger and healthier they are, the longer they will last. Strength training is great for maintaining both muscle and bone strength, which are imperitive in allowing the elderly to perform normal tasks of every day living and preventing fractures due to fragile bones.
Flexibility exercises are excellent for preventing stiff and immobile joints.
As we get older our joints tend to stiffen due to a reduction in activity and various physiological effects of aging. So in order to keep those joints from aching everytime you move, get yourself involved in a flexibility program and make all the creaks, snaps, crackles, and pops go away. Maintain the exercise. Don't just exercise for a few weeks and think that you've done enough. Regular physical activity needs to be a part of your every day life and should almost become just another part of your day, like eating breakfast or dinner.