Who says you can't write about celebrities? Who says you can live in worlds that don't exist? Who says you can't be a mermaid? Or kiss the hot guy you've been head over heels for since you set eyes on him? Who says you can't visit that one place you saw on Tumblr that one time? 
I say you can do all those things and more. Anything is possible if you set you eyes on it and get moving. Never miss the opportunity because someone says you'll never succeed. Prove them all wrong and don't follow the crowd. Just because that girl you hang out with orders a  Venti Caramel Frappie with extra whip and drizzle, doesn't mean you have to! Be your own person with your own amazing dreams. Be the girl every boy secretly loves. Be the guy ever girl dreams of marrying. No one else can be you as good as you can so don't try to be them. 
What I'm saying is, it's your story, don't let someone else write it for you.