A slideshow at the NY Post shows participants from the "world's largest swinging convention" held in New Orleans, and the average age looks like 50 to 60. The one woman who was under 40 was photographed twice in a desperate attempt to make it look not so geriatric.
The under-50 generations may be more likely to "support" deviance of many kinds, but less likely to actually practice them. Boomer women are sluts, while Gen X and Millennial women are thots (attention whores).
What is the appeal of swingers' clubs? It's related to the outgoing social atmosphere, rather than the cocooning one. Swingers are not simply couples who have open relationships -- they want to meet up in the same location and get it on in a crowd setting, unlike doing it in the privacy of your own home.
They seem to get a rush from feeding off of all the other activity going on around them. This preference also drove the trend of orgy scenes in old porno movies.
It may also help with their self-consciousness, losing themselves in a faceless crowd in the dark, similar to dancing in a nightclub rather than dancing with only your partner in the room at home. The herd mindset helps them get over their inhibitions -- they feel like they're just passively conforming to the environment, not choosing to act out.
This need to overcome inhibitions and remove personal responsibility is common to deviance, showing up also among gays, who prefer dark faceless crowd settings to suppress the awareness that what they're doing is wrong (everybody else is doing it, as it were, so it can't be wrong).
Swingers' clubs took off during the Disco era, and pictures from the time show the couples to be mostly 30-somethings. Those would be the Silent Generation, who also made up the bulk of the hippie and counter-culture phenomenon a decade earlier (Boomers were still in school). The Silents were raised during the cocooning Midcentury, and were the most desperate to indulge themselves once the zeitgeist became more outgoing, fun-loving, and rising in crime rates circa 1960. They were also the ones who made up the divorce epidemic of the time.
Well, 40 years later and the average birth year of swingers has only budged 10 to 20 years later than the Silents. That shows a strong cohort effect that lasts throughout the lifetimes of the Silent and Boomer generations (together the Me Generation), who became adults during the outgoing and rising-crime period of roughly 1960 to 1990.
Gen X and Millennials, who became adults during the cocooning and falling-crime period of roughly 1990 to present, did not socially imprint on a climate of "if it feels good, do it". However, when the climate does become outgoing and rising-crime again, the Millennials will repeat the history of their Silent Gen counter-parts, who were raised by helicopter parents and socially sheltered, and who will jump at the first chance to lose control when the culture finally does change to a more freewheeling zeitgeist.
Gen X, like their Greatest Gen counter-parts, will be too old to get in on the surge of degeneracy among 30-somethings, who by that time will be Millennials.
I explored these themes in depth during 2010-2012 (see the archive at the right of the page), if you've only started reading here during the past few years. Here are related posts on the decline in flashing and streaking, and the graying of nudists who cannot recruit anyone under 40.