Most Helpful Girl
Never compare yourself to a celebrity. A lot of them have work done, they have chefs, and trainers to help them maintain or get a nice physique. You an the average woman.
At 5'7 and 120 lbs you are not fat, actually you are quite slim.
It is true, as you get older your metabolism tends to slow down and you gain weight. But at 21 or 22 I am sure you will look pretty much the same , this usually happens with people that are a little older (I heard metabolism slowing down happens around 30 or so.)
Maintain a healthy diet and plenty of exercise. With that you won't have anything to worry about.