As Emma Waring, a psychosexual nurse and author of Seasons of Sex and Intimacy tells me, for the young couples she's increasingly working with, "sex is at the bottom of the to-do list, they never quite get there".
In my network of close friends, a few are still single. For the one currently travelling the globe, sex is as liberating and exciting as the salsa lessons across Colombia. For the rest, sex is just not a priority.
Received wisdom would have it that the internet has made casual sexual encounters as easy to come by as a coffee shop on a High Street, but even in our taboo-free, app-heavy culture, finding sex when you're single can be harder than some might imagine.
"Most of my single friends are largely celibate, maybe one partner every year," says Rachel, 24. "That's why I find it so baffling in Friends, when they're like, 'Oh, you haven't had sex in a month?' Loads of my single friends haven't had sex in eight months!"
Michael, also 24, tells me, "The last relationship I was in, we had sex regularly, a lot, even. But I had this idea that when I became single I would starting having sex with lots of different people."
This has not been the case. Hook-ups are "demanding of time and effort" and he doesn't like using apps: "The idea that I would have to meet up with loads of [the women behind] these text conversations to find if any of them were genuine 'connections' seemed like a big job".
This is what Julian termed the 'Tinder Mirage'. Essentially: "Unless you are especially good looking, the thing online dating may be best at, is sucking up large amounts of time," she writes. "
As of 2014, when Tinder last released such data, the average user logged in 11 times... for a total of about an hour and half a day. Yet they didn't get much in return. Today, the company says it logs 1.6 billion swipes a day, and just 26 million matches."
I can testify to this; when I was using the dating app, Happn, I had to take it off my phone and install it on an old iPad which never left my flat instead, in an effort to streamline usage.
I was wasting so much time on a sea of indeterminable faces, which was not only unproductive, but wildly depressing and certainly didn't want to make me run out and have sex with the closest one I could find. This in part, leads to a paradox of choice: "so haunted" are young people by this endless sea of faces, says Julian, that they "don't make it off the couch".
And there's another paradox; as much as most of us hate using dating apps, meeting anyone in real life (IRL) is perceived to be increasingly impossible. Arielle, 23, tells me she recently threw a house party where nobody went home with anyone, even though they had been chatting to people they later revealed they liked.
"People are afraid," she says. "We're a more over thinking and anxious generation and it's much safer to do this online". Anna, 24, agrees, "30 years ago you had no choice, but it's much easier behind the security of a screen".
The other big internet-driven issue which may be preventing young people from having sex is porn. "I certainly ask couples about pornography in a way now I didn't 10 years ago," says Waring, who notes men increasingly recognise the addictive damage done as they seek greater and greater hits.
"Suddenly," says Waring, "the person they are actually in bed with just can't cut it". For Michael, turning to porn as dating replacement left him "feeling dissatisfied and actually very sad".
In trying to understand the sex recession, or even framing it as such, however, Professor Jacqui Gabb, a sociologist researching intimacy and sexuality, wonders if we're asking the right questions.
"If young people are having less sex," she says, offering some reservations about how data is collected, "what I'd like to know more about is if they are having better sex, and I don't mean more orgasms. I mean sex that has a better meaning to them."
Living with family or in shared housing with friends for longer, for example, could mean they are getting greater support from peers than partners, compared to previous generations. "It might be that young people are finding they can have intimate attachments without sex," she suggests.
So it's not necessarily all doom and gloom. Perhaps if young people are finding a healthier relationship to sex, one that works for them and reflects the moment we're in, "recession" isn't really the word we're after.
I was hopeful to hear from Anna, who has happily rejected one-night-stands and is sanguine about not having more sex. "I have a nonchalant approach," she says, "I will do my own thing until someone is good enough for me to want to invest in them."
And what about the midlife sex drought?
Rowan Pelling writes: I met up with a bunch of old friends at a 50th birthday party recently and as the wine flowed our conversation descended into competitive banter about who was having the least sex.
The reasons varied. One woman had a sick partner, another shared her bed with her six-year-old daughter rather than her husband, while for many, several decades with the same person meant familiarity had bred ennui.
As US relationship guru Esther Perel tirelessly points out, we demand too much of our other halves in modern life, requiring them to be best friends, soul mates, co-parents and red hot lovers, while somehow maintaining erotic mystique.
Back here on Planet Reality the only people regularly getting their rocks off seem to be the second-time-newly-wed and those with secret lovers.
The evidence isn't just anecdotal. The National Survey of Sexual Attitudes and Lifestyles (NATSAL) has been quizzing Brits about intimacy since 1990 and in its 2010-12 survey recorded a distinct downturn in the frequency with which Britons make love – leading to jokes about bromide in the water.
Either way, the dearth of sex amongst middle-aged Brits seems so pervasive you can't help feeling it warrants its own hashtag campaign. I suggest #NeitherAmI.
So what's going on? It's hard to ignore the fact we have no clear divide any more between our public and private space, taking tablets and smart phones to bed with us – allowing out attention to wander off to social media alerts when we should be tuning our radar to our spouse.
Nextflix is another culprit. I can't be the only person who often finds themselves opting for yet another episode of The Crown, or Game of Thrones, rather than an early, sexy night. (Although – top tip – The Haunting of Hill House is so terrifying you have to seek solace in the arms of your beloved after viewing.)
Then there's the fact people of my generation tended to have children much later than their own parents, meaning emotional demands still centre round offspring. We can be too drained by child-rearing to muster the enthusiasm for adult passion.
If you're not drained by kids, chances are you'll have an ageing parent or two to fret about. Add to all this the pressures of the working day, which rudely intrudes its creeping tendrils well beyond the parameters of nine-to-five and suddenly couples are composing emails in bed – nobody's idea of great foreplay.
Even the singletons aren't having as much sex as you'd fondly imagine, tiring of Tinder dates and sad one-night-stands. This all makes for such a stressful life that some reach for booze, other for anti-depressants – both known culprits in depleted libido.
Good sex requires time, energy, enthusiasm and opportunity and currently we channel those limited commodities everywhere but under the duvet.
