Even though I have grown, I can't imagine that I have grown

I'm going to be 20 next year. I still can't understand how and when did time fly by so fast? Like 20????? I seriously cannot understand this at all. All I remember is being 14, attending classes, crushing on celebrities, listening to songs and etc. hard to believe in 5-6 years I'll probably get married, and it's just really hard to believe that I'm going to turn 20. I cannot understand the responsibilities that I have now, and that's really interfering with my work. Can't concentrate. Idk what is happening. Please help