> People in their 20s having their own digs is, I think, a decidedly American phenomenon. In most of the poorer parts of the world (including, for example, Central and Eastern Europe), 30+ years ago younger crowd managed to have sex just fine, using dorm rooms, snatching time while parents were away, etc.
I think them not having their own digs is much more an American phenomenon, at least recently. Though houses have gotten ridiculously expensive in a lot of countries. Still, back when I was in my 20s, it was quite common in Europe for people to at least rent their own place, and possibly even buy a small apartment. I've got an entire branch of my family where everybody married at 21 and moved out at that age. In my parents' time, it was not much different, though they did live in my grandparents' massive house briefly after their marriage, and bought their first home when they were 34. But it was definitely common for people to move out of their parents' home when they got married. Once going to university got more common, that became the time they moved out.