When you get down to it, Calorie balance rules the day.
Basal Metabolic Rate is the rate at which you burn calories if you laid flat in your bed and stare at the ceiling. Responsible for 60-75% of calories. Muscle mass determines Basal metabolic rate. Men have more lean mass than women. We lose about 3% of muscle mass per year(sarcopenia). As you age you are losing lean mass and you atrophy faster if you don’t move.
If you need 2000 and eat 100 calories a day more, you will gain 10 lbs a year.