I have looked younger than my age, at least since college. I have frequently been mistaken for a high school student (which is frustrating when you are in graduate school). Just last week I was in the Department of Public Safety (where you go to get your drivers license in Texas), and three people commented on how much I must be looking forward to getting my learners permit (I received my learners permit ten years ago).
I hope this does not continue as I am finishing the certification to be a high school teacher, and I do not want to be thought of as being the same age as my students, or as being a student.