Please don't be serious.
It's okay for you to enjoy anime at that age.
It's okay for you to be in an anime club at that age. Even if you went to conventions, that'd still be perfectly fine.
But you are not a child anymore. You're interested in a form of entertainment whose demographic is largely people 20 and under. Yes, it would be creepy for you to approach this girl. She is still a child, especially relative to yourself.
Find people your own age.
You might have to grow up. Don't be afraid.
Just step out of your comfort zone.