Is It Your Choice (most of the time) If You Don't Have Any Friends & You're 23?

My brother is 23...I feel like he has friends cause I can tell by his Facebook profile, but he never, ever, ever hangs out with anyone. I don't get it because based on his Facebook wall, there are always comments, posts, etc. I don't quite get it. He just seems so lonely to me, always has, and it makes me really fuc*ing sad cause I don't know if he doesn't have any friends because of his own choice/doesn't wanna hang out with anyone or if people don't like hanging out with him. He never talks about any of his friends EVER, yet he has more Facebook friends than I do. Not like that means EVERYTHING, but you know where I'm getting at. I can't grasp this... And it's not exactly the type of a question a lonely person wants to hear.. "why don't you have friends?"...It just makes me sad...what do you think?