Fat cells are an important contributor to aging1. To stay as healthy as possible you have to keep your weight under control2. Your optimum weight is such that your BMI is between 20 and 25 and the lower within that range, the better.
If you’re interested in living a longer and healthier life, try eating fewer calories. Forget about the 2000/2500 kcal/day you hear about everywhere: whether you are eating enough calories is clear when you step on the scale. The important thing you need to keep an eye on is eating a good mix of protein, carbs and fat and ensuring you get enough of all essential vitamins and minerals. Some folks manage that on 1500 kcal/day (sometimes with the help of some supplements) , at which point you are far into the practice of calorie restriction.
If you are really serious about living a longer and healthier life, also look into intermittent fasting. Apart from automatically reducing your calorie intake, fasting has independent health benefits. There are several ways to practice intermittent fasting, some of which can be combined. One easy, but costly, way to fast for a longer period (5 days) is via Valter Longo’s ProLon diet3,4, but there are many ways to achieve most of the same effects in other ways.