Should I try to start a relationship?

Okay, so there's this guy. But he's a bit older than I am (i am 15, he is 17 or 18) He made out with a girl in my grade, so i know that age isn't a problem with him. He is super nice, and extremely fun to be around! He has some characteristic that seems to bond people to him, his presence is warm and inviting, like a fireplace on Christmas Eve. He puts his arm around me a lot, but he does that to other people too. He has a never ending confidence level, so Idon'tt know how to tell if he likes me as a friend, or more than that. However, on the first day I met him he seemed to be checking me out, and im not the most attractive person in my opinion (never been asked out) So do you think he likes me? should I flirt alittle? how should I flirt? I only see him up to three times a month, so how can I make an impression? The longest, most thoroughh answer wins :D pleeeaeee heeellllllppp!