On the topic of, "What are the implications of men and women waiting until much older to have children?", one thing I almost never see brought up is the extremely skewed sex ratio of children born to older parents.
For those who don't know, it's been found that as both men and women get older,
their likelihood of having a daughter increases, going from a 51:49 boy-girl odds in the early/mid 20s to a whopping 35:65 boy-girl odds by 40. That means that parents aged 40 and older are almost TWICE AS LIKELY TO HAVE DAUGHTERS THAN SONS. And this affect is cumulative; it's not like the ratio suddenly jumps from 51:49 to 35:65 at age 40; with every year you delay past your early/mid 20s, your odds of having a daughter slightly increase while your odds of a son slightly decrease.
There are two interesting things to this phenomenon: the causes and the societal implications. First of all, the causes:
The X-chromosome is about 10-12x larger than the Y-chromosome. Because of this, the Y-chromosome is much more fragile than the X-chromosome. This isn't a big deal when the father is young and all of his sperm are healthy, but as he gets older and his sperm get less robust, the Y-sperm are the ones disproportionately affected by this aging. They are much more likely to fail to reach the uterus before "dying" as compared to more solid X-sperm, and even if they do make it and fertilize an egg, they are far more prone to catastrophic breakages on the journey there and thus more likely to result in a miscarried fetus due to genetic abnormalities.
While the father's sperm ultimately determines the sex, there's also evidence that older women experience hormonal changes that may influence the pH of the vagina which disproportionately favor X-sperm as compared to weaker and more vulnerable Y-sperm. So even older mothers are more likely to have daughters independent of the age of their male partner (though the effect is far more pronounced for older fathers than it is for older mothers), and vice versa.
So, what are the societal implications of a massively skewed sex ration in favor of women and girls? Well, politically and economically speaking, you can expect everything to swing more left-wing. Co-ed schools being unsuitable for boys will only get worse as there are significantly more girls than boys in classrooms. Crime rates and homelessness rates might go down, but social services will still be strained due to the fact that women live longer than men (and are thus a greater burden on social security). An optimist might say that a surplus of women compared to men might help even out the dating scene and make it easier for young men to secure partners, but considering the extremely polarizing gender politics pitting women against men, I kind of doubt it.
Crucially, older parents are also more likely to be wealthier than younger parents and are more likely to only have one child they can pass all of that on to -- their daughter. This might mean that young women become disproportionately wealthy as compared to young men on average, and in general have a better start to life and greater access to resources than young men do, thus only further widening the gap between men and women.
While the mean age at first birth is still low enough in most nations that this effect (to my knowledge) hasn't really made itself known yet, the trend of people continuing to put off children as long as biologically possible only seems to be accelerating, with more and more people not even considering having children until their 30s. Maybe we'll see this trend begin to make itself known within the next few decades.
Edit: Can someone archive the article for me? It isn't cooperating with me for some reason.