Feeling old at 20.....

Ever since i turned twenty in May, i got this feeling that i'm getting "old". On the night of my brother and i's birthday (fraternal twin), he said that we were going to be thirty in just ten years. Now i realize that i'm still very young, but i'm just surprised how "fast" it went. It being life. Looking back on what i've done so far with my life, i realize what little i've accomplished so far.

So has anyone, who is still young, ever felt like this before?