Caloric requirements vary according to age, gender, activity level and even climate. For more information, see the link below.
a kid needs about 1,800 calories. but if your fit you need about 2,000
As you get older you generally need less calories to maintain weight but that is only because as the average person gets older their metabolisms slow down and they tend to be less active, but...
i am not sure but one mac donalds is the full amount of calories you need in a day
In one day to get your full fiber you need about 25-30grams a day.