> Another thing that caught my attention is that my female friends all have active social lives, whereas that is very rare among the men I know (again, past a certain age).

Yes, that is a pretty typical thing. Starting around late 20s, pretty much most guys are either part of a steady relationship, usually with kids or permanently without a relationship. The men with families have their own family events and get included in the wife's social and family circle. The guys who do not get paired up are not welcome at those events and wives forbid the partnered up guys to hang out with their single male friends on the other days. To be fair, there is nowadays anyway so much online entertainment, that it probably will be fine in the end.