I'm in my thirties now and sometimes it feels like there's plenty of time to figure this out. But most of my closest friends are somewhat older than me. Almost none of them have started a family in the traditional sense. Most of the people they were friends with drifted of in their own little family worlds over time. Another good chunk of former friends pursued professional/academic careers which led them to move quite some distances.
And I can really understand their fear that the younger people they befriended (like me) will do the same (which I and my long-term partner are ruling out but they heard a lot of people saying that before doing it anyway).
I find it comforting that we talk about this from time to time and try to reassure each other that there will be a shared future as we get all older together.And I sometimes think this wouldn't happen if we were all the same age. It kind of helps getting the perspective of older friends which have lost track of a whole lot of people during their lifes. At my current age I can feel the impacts getting closer. It's oftentimes a really short way from "friends for life" to "acquaintances from the past".
And I wouldn't mind at all if the roomate analogy of the author would be literally that shared future:
> It’s not dissimilar to a big house with lots of roommates, or even a college dorm — it’s just that the living areas are separated by a few blocks instead of a few feet.