Staying fit as you age also becomes more difficult. The diet I’ve settled on as the one being most effective is a macro based diet.
I do the 30/40/30 macro plan. This is basically 30% of your calories from carbs, 40% from protein and 30% from fat. I do about 200-300 calories less than I burn per day.
The app I recommend using to track your calories is MyFitnessPal.
Here is a calculator to help you calculate how many calories you’d need to eat per day to lose weight: