How do i flirt with a guy that is younger than me and who is my friends brother?

im 14 nearly 15. Recently i met one of my friends brothers....he is 13 and i really like him....just everything about him. Problem is he's one of my best friends brothers and he is also younger than me. I don't no if this would be weird? Also im really really shy around guys so i dont no how to subtly flirt with him......I dont know what to do about my friend.