This gets especially hard if you are childfree and content. Odds are, the male friends you could make in middle age have had children, and that is much of what they talk about and it determines what free time they have to hang out. It is easy to feel like you and them are living in completely separate worlds, and if you detest children to the point you don't even want to hear about them, it makes conversation tiresome. This is why the fraternal society or pub/cafe culture route doesn't work for me.