17 year old girl + 26 year old man?

when I first started liking this man he was 24 and i was 15 he's an old family friend and he flirts with me nonstop. I know I shouldn't like him but I do. Is there something wrong with me? I guess its not right (which I would like to know why) As it happens I know hes attracted to me ( I don't exactly look 17) and I would like to know other peoples opinions about all this