20+ and look too young for your age

I am 21 years old but I get mistaken for a middle schooler quite often. I cannot go anywhere without me showing my ID. I really dislike it because it's the first comment out of peoples mouths and they keep bringing it up and giving me a hard time. I don't act immaturely nor do I dress immaturely either but it's just my face that is the problem. I have chubby cheeks with a small face so it makes me look younger.

I just want to know if anyone else goes through this??? It is very frustrating because you don't get treated like an adult rather a child.