I like a girl…

(Im 14, she is 15 and my classmate) I dont know how to talk to her, should i write her?, should I wait?(to get a girl when I'll be older)I just, dont want to, like, leave her behind, because she looks pretty nice.
. I feel shy to express my feelings to a girl. Thanks for any advice.

EDIT: she once said that for future she'd want a tall and physically strong bf and that i am.