There are several factors which people use to judge the apparent age of a person. Chubby cheeks are not one of them. Take a look at people on the street and notice that being overweight doesn't make a person look younger.
As far as your weight goes, you are average for your height and age. I don't recommend that you try losing weight while you are developing. Many diets are not well balanced and the lack of proper nutrition can interfere with your growth. At the very most, I can suggest cutting back on deserts, sweets, and the like to see if that lowers your weight a bit, but you might not be able to tell because you are still growing. So while the scales don't show a decrease in your weight, you might still be slimming down.
What people look at is the shape of a man's jaw and the texture of his skin. I suspect that you are in stage 3 of development. It is in stage 4 that the shape of your face begins to change. It is also in stage 4 that you will begin growing darker facial hair. Those two things will make you look older. So, be patient. It will come in time.

