I think it varies by place and culture. I live in Turkey and hetero male to male touching is more accepted than in N. America. The normal greeting between friends is a handshake and a double 'kiss' on the cheeks. It's not really a kiss, just a light touching of the cheeks with a quiet 'tch' sound. The more macho version is a double butt on each side of the head.

It's very normal for same sex friends of all ages to walk with linked arms, but never, ever holding hands. Also a draped arm across the shoulders is very normal. Or you may hold another guy by the bicep or elbow, put your heads close and talk in his ear when you want some privacy. I like the sense of intimacy that this contact between friends confers.

At first, I sometimes popped a boner, but now I am use to it and it's just part of the scene.