Eating well is important at any age, but becomes more so as we age.  It seems that young adults can eat nearly anything without any consequence.  But as the years go on, foods have more of an effect on a body.  Eating well-balanced meals is important to avoid conditions such as type 2 diabetes and high blood pressure.
Food is essentially energy that the cells in our body need to do their jobs.  So we need to eat enough to give those cells the energy that they need.  As we age and are not as physical, our cells don’t need as much fuel and so we do not need to eat as much.  But fewer calories do not mean fewer nutrients.
Nutrients are those vitamins and minerals that our body needs.  Some of these are stored in our body, but many are not.  This means that we need to regularly eat these nutrients to supply our body with the materials to help it function well.
So where do we find those valuable nutrients?  Fruits and vegetables are excellent sources, especially green leafy veggies packed with nutrients such as iron.  Fortified breads and cereals have fiber as well as many vitamins.  Milk and juices have many more nutrients than calorie-laden soda.
So choose your food wisely and seek a good nutrient-calorie balance.  If you are concerned about finding that balance, seek the guidance of a nutritionist.  A nutritionist can produce meal plans just for you so that you can eat your healthiest.