Dear Elizabeth, With an older sister over 100 you definitely have the right genes on your side. I am not sure I could pick one "perfect food", or even one perfect food group. I can however make some broad recommendations, and let you decide which fits into your diet best. Of course, with aging, food volume and food intake generally decrease. Therefore, selecting foods with high nutrient density is a priority. Not caloric density rather nutrient density. Foods which contain a large amount and variety of essential nutrients that are low in calories. And foods with the biggest "bang for the buck" are those from the fruit and vegetable food groups. Eat these as often and as varied as you can. Eat them from all over the world, all different colors, shapes and textures. There are over 4000 phytonutrients (phyto - plant) which thus far have been discovered and more probably exist. 
Phytonutrients are powerful chemicals, which provide numerous health benefits including potent antioxidant properties. Fruits and vegetables are also loaded with water and fiber - two essential yet under rated and under eaten nutrients in our society, particularly among seniors. Fruits and vegetables are also very low in fat, particularly saturated (bad) fatty acids and devoid of cholesterol. So Elizabeth, my recommendation to you would be to eat more fruits and veggies and stay away from as much processed, high-fat, high-calorie foods as possible. In doing so, the only reason you might need a supplement would be the correct reason - to supplement an already healthy diet, not to make up for a poor one! | 
