What changes are needed to an elderly person's diet?

Less calories. As we age, we typically become less active, although ideally we'd actually strive to maintain our previous activity level. But for the average joe(sephine), our metabolism slows down. As such we don't need as many calories as we once consumed. On the other hand, we still need to consume plenty of water & fiber. Dash diet & mediterranean diet are both excellent choices regardless of age.