Haven't Changed

Walking home from class today I realized something very important about myself.
Maybe I'm the only one but my self image doesn't evolve as quickly as I do.
I'm 21, out of high school for nearly 3 years and my self image is still of that girl I was in high school.
I don't see myself as an adult... I feel out of place in a room of adults, and when I'm at the bar I feel like I'm breaking the rules. When adults talk to me like I'm an equal it confuses me. I still start shaking when I talk to teachers and professors. I feel like I'm still a awkward teen stuck.
I don't know why my self image hasn't evolved.
Even around my peers I feel like a child among college students.
Why is this?
I don't have an answer but I wish I did. I can handle myself amongst adults, and I can deal with just about any situation I'm in. But inside I still feel like a little kid or an awkward teen.
Maybe eventually my inside will evolve to the same level as my outside?