I assume you're joking here, but anyway, I wouldn't say there's huge singles contingent among older WCS dancers. Probably about half come as couples.
It is true, though, that around here, the west coast swing folks, while not necessarily "elderly", tend to be older than the tangueros by a decade or so. Both are substantially older than most of the ballroom crowd or the salsa crowd, though ballroom has a pretty big age range.
Your assessment of how much mixing each community has is consistent with what I've observed.