Where does the time go?

Next week I turn 20 years old and it freaks my freak to think about. When I think of someone who is 20 years of age I think of a mature grown up. Ha. I'm so not that. Feels like just yesterday that I was going into junior high. Strange. I don't like how fast time goes by. And I REALLY don't like being a grown up, or I guess I should say, the thought of being a grown up. All of my friends are turning 21 soon, and because I'm the youngest of my class, I'm still only 19. I really don't want to lose that "teen" of 19. It freaks me out. I know that technically I became an adult at 18 but come on, in my mind if "teen" is still in your age then you are still a teenager. And I suppose at 18 you are still a teenager, you just have legal responsibility. In my personal opinion, I don't think you should ever be expected to 'grow up'. Be responsible? Yes. But grow up? No. But in our society, we suck the inner child right out of ya! Heck, your brain doesn't even fully develop until age 25!! Anyway my point is, is that age 20 freaks my freak. Maybe I'm having a quarter-life crisis? I just don't think I'm up to par in "grown up" points as the typical 20 year old. But heck, I'm responsible and I have a good time. So I guess that life is good!
 Maybe I should buy a manual on growing up and how to act like an adult!?! Do they sell those? ;)