So what you're saying is, young people are having less sex, because they're having more sex?
(take this as tongue-in-cheek, I don't think you're really making that argument)
I thought that was because they spent their 20s-30s focusing on college and their careers, and just as they had extremely high standards for those, they also had extremely high standards for men they dated, so they ended up not "settling" for anyone.
I'm just over 40 and have dated a few of these urban-dwelling women who 40 and up, never married, no kids. There's a ridiculous number of them in DC. In my estimation based on personal experience, they're all incredibly picky and won't date a guy unless everything is absolutely perfect. In my case they tend to lose interest very fast because I live outside the city presently so I'm not conveniently located. To be snarky, they seem to all want a guy who's over 6' tall, looks like a model, dresses like he's on the cover of GQ, makes $300k/year, and lives across the street from her. And I actually meet a couple of these criteria to some extent: I'm over 6' (which seems to be very rare here on the east coast I've noticed...), I have a good-paying job (though not $300k/year good), and I'm told I'm very attractive, particularly for an over-40 guy as I'm thin and in great shape and frequently confused for someone 10+ years younger; my deficiencies are that I don't dress like a GQ model (more like an engineer who wears polo shirts all the time), I'm not outgoing and gregarious (I'm a software engineer....), and I don't live in the hip part of town these women all live in. The last such woman that seemed to be seriously interested in me (a 40yo lawyer) dumped me after a few weeks because of the distance, or so she said, even though this was something she knew about up-front. Oh yeah, these women also don't like guys who are separated or recently divorced (good lucking finding a decent guy at 40+ who's never been married or was divorced years ago). And AFAICT, they are not quick to jump into bed with someone, in fact quite the opposite (and these are not conservative religious women either, they're all liberal Democrats AFAICT, though really more like "limousine liberals"). Sorry for the rambling, but the thing about single, childless, pretty women in their 40s is something I have recent and direct experience with so I couldn't help going off.
Are these friends of yours in or near metro areas? If so, which one(s)? From my research, if you're a single guy in the Bay Area, you'd better be happy with celibacy, and Seattle isn't much better. But NYC and DC are full of single 35-45 women (but they're all incredibly picky IMO as I said before). The problem, however, is that if your friends are all software engineers, they're more likely to be in cities that have more men than women. NYC just isn't a very good place for a SW engineer, unless you love finance and HFT (and what I read about the work environments in those places is not good, and you'll have no free time for dating anyway), or web development. DC is mostly defense-related stuff, and in my experience there, the defense stuff is all well outside the city proper (defense contractors are cheap bastards I guess), whereas all the upper-middle-class single women live in Georgetown or near Dupont Circle or something, since they all work downtown or at the university, so you're looking at a minimum 45-minute drive to visit each other.
I'm rapidly coming to the conclusion that software engineering is an absolutely horrible profession to get into if you're a hetero male who isn't an ultra-conservative churchgoer and wants to be able to date attractive professional women: it places you in locations that are far from these women, and keeps you in social circles that are completely alien to them, and in work environments that are devoid of any such women. I really wish I had gone into the medical field instead, honestly. In my experience, engineering is a great field if you're either an ultra-conservative religious person who wants a stay-at-home wife in a low cost-of-living region, or you're asexual and want to live in Silicon Valley and dedicate your life to work.