He’s not a rule-follower or particularly organized. We know this by the amount of school tardy slips he’s racked up. He’s not chivalrous; he leaves his unconscious beloved unattended on a porch swing in a dicey neighborhood. He’s a loyal friend and well-liked by strangers. He’s fairly athletic, riding multiple iterations of a skateboard with ease. If it weren’t for the tardy thing I’d call him a One. He has a certain can-do attitude and a love of adventure that might indicate a Seven. His ability to charm the past and come out a winner, and his hatred of being unfairly labeled a “chicken”, suggests a Three. So, what have we got?
He’s not interested in how Doc invents things. He doesn’t chime in or brainstorm, or even try to understand. Not a Seven.
Besides being a time traveler, Marty really has no vocational plan. What did he like to do before Doc intervened? Drive a 4×4 is about it. Not a Three.
He’s a man who needs a mission, and when it’s given to him — save the past to save the future — he’s engaged and active. The tardies are a sign he’s drifting, looking for that motivating moment to come from outside himself and change his life. One.