Stupid question: is it ok to add him on Facebook?

[steeprainstorm636]

So my brother is 10 years older than me. He is 25 while I am 15. His friend started to come over my house and always try's to teach me things and stuff. So the one day he was over a guy came and knocked for me. When I left with this guy my bros friend came out and said he better not be your boyfriend your to young to have a boyfriend and all this stuff. Basically he acts like a very protective brother to me but I hardly know him. Would it be weird for me to add him on facebook? Or does it seem like it would be ok? I know it's dumb but I don't want to have it be awkward and him say to my brother something like you're sister tried to add my on Facebook and think I'm completely weird. I know it's really dumb but just let me know what you think.