The nutrition problem is different in different age groups. In the elderly, the problem is not that these people eat less, rather it lies in the fact that they don’t get enough nutrients. Moreover, with age, people become vulnerable to different diseases that may result in malnutrition. It may also be possible that poor nutrition in the elderly causes chronic illness. So, in both cases, nutrition and disease go hand in hand.
There seems to be no general consensus about when old age actually begins. The United Nations has generally denoted old age as beginning at sixty-five, in agreement with most countries in the developed world. But the World Health Organization has established age 55 as the beginning of old age in Africa. So, as you can see, it all depends on the culture in which you exist. Old age is relative. But science has identified many factors which may define our old age, and none of these are calendar related.