I have an older brother (21 months older) and he and I don't really have much of a relationship. We live about 15 minutes apart, but we really only see each other when we need dogsitting services or during the holidays.
We had a lot of rivalry when we were kids, but I think that as adults, it's just more that we don't have a lot in common. I don't think we're each other's "type," and if we weren't siblings, I doubt we would choose to be friends. You know what I mean?
(It's not that I don't like him. I think he's smart and hysterically funny. Seriously...he's the funniest person I've ever known in real life. But we have very different personalities, likes, interests, etc. We always get along great when we're together. We just aren't together very often...don't choose to get together. And I also think it's probably accurate to say that I like my brother more than he likes me.)