should I add him as a friend on facebook? I want to but its a tough decision?

[FriendlyScholar564]

I go to a high school where the middle school and high school are both connected to each other in one building. I'm a 9th grader and theres this 7th grade guy that I met that is very nice. he will say hi to me in the hallways, he likes me but not in a romantic way thank goodness. Hes a very nice guy but I'm afraid to add him as a friend on facebook. other people in my grade and other people that are older than me added him on there.Every time he would see me in the hallway he would smile and say hi to me, we carried on a conversation before, hes like a little brother to me. I don't like him romantically
so do you think I should add him on facebook, would it be strange for a 9th grader to add a 7th grader on facebook, and again I'm in high school and an 11th grader and a 12th grader are on my facebook.
so I'm not sure what to do.