In a research article published in Cell Press, Australian researchers indicated that although a high protein diet may be harmful for people between the ages of 50 and 65, it might be more beneficial for people over the age of 65.
http://www.cell.com/cell-metabolism/retrieve/pii/S155041311400062X
The cellular biologists concluded that in fact, a high protein diet for those over 65 may protect them from cancer and also from frailty caused by sarcopenia (muscle wasting).
The researchers recommended that people over age 65 gradually increase their protein and preferably eat a mostly plant based diet to allow the maintenance of a healthy weight.
Good sources of plant-based protein are beans, peas, nuts, seeds, peanuts and peanut butter and soy products like soy milk, tofu and tempeh.