I'm 19. Oh no.

This may sound totally ridiculous but I can't believe that I am 19. TIME FLIES. Parents, grandparents, teachers, everyone warns you but you don't believe it when you're young and free. I am now in my last year of being a teenager and it SUCKS. Inside I am still a silly, immature 14 year old who just wants to have a laugh with her friends and listen to angsty music. I do not feel in the slightest way prepared for impending adulthood. 
18 was a comfortable age, I could now legally do everything I'd been doing for years before and yet could still act silly and have my meals cooked for me. University has, of course, been a maturing experience. I have learnt lots, become much more independent and (a little bit) more sensible. But not enough. People have kids when they are 16, there are glamour models who are 17 and people moving out to live alone when they are 18. I can simply not imagine doing this.
I don't think it's necessarily just me either. Obviously, there are plenty more people who are much more mature and sensible than me but many are just the same as myself. 19 is an age at which you know that soon you are going to be in the most exciting decade of your life. This is the decade when a career becomes clear to you, you may get engaged/married and have a child or two, you know who your lifelong friends are, you have travelled the world etc. It seems to all happen.
I don't feel at the stage of my life yet, I feel like I still need to experience many more things before I can fully be in control of my future. I've always said if I could stay at one age, it would probably be 21 (even though I haven't experienced being 21 yet) but if I can't manage being 19, how can that possibly be true?!
Maybe this is all a big overreaction. They said age is just a number after all but society, whatever you say, has innate connotations with ages. 18 - exciting. 21- an adult. 30- reaching maturity. 40- life is just beginning. 50- half a century and so on. 19 isn't seen as a milestone age but it IS the last year (as some see it) of teenage freedom, of being able to have strops and fits because "you're just a teenager." 20, to me, just sounds SO OLD. 
Anyway, that is my little panic over with. I'm sure there are those of you out there who are over 19 and as youthful as ever. I aspire to be like you.
Xo.