I'm terrified of getting old

Whenever people guess my age, they always guess a couple of years over of what I am. The last time a girl I know (17) asked me how old I was, I told her to guess, and she said twenty. I'm 18. It ruined my evening.

I don't want to look older than I am. I don't want to get older than I am. I want to be 16 forever. .____.