Is it okay for a elderly to eat more food to be healthy?

I don't think so. It does not matter how much you eat but what you eat. People at all ages need energy for daily performance, which are taken from foods. However, according to many factors, like age, gender, job, etc. each person has their own amount of foods to eat.
The elderly should have an increased intake of calcium for healthy bone. They should also consume foods which assist memory like fish oil, coconut oil, blueberries, cinnamon, honey, etc.