I think near the end when the youngest person is 40-50 it would collapse, but not when the youngest person is 20.
Hell I’d think the youngest people would get a kick out of it, screw all you want no worries about pregnancy? SHWEET!
I don’t buy that, given the 20 year-olds were raised in societies that were increasingly desperate to solve their lack-of-babies problem. Pregnancy wouldn’t be seen as any kind of burden, but a much-desired blessing.
As an incidental, I was baffled by the popular appeal of Children of Men and said so at length at the time. I thought it was a terrible movie, certainly not any kind of plausible blueprint for the collapse of civilization.
I try not to analyze allegories. They always fall apart when compared to how “real people” would react in the circumstances.
One thing that bugged me was that any couple with even one child isn’t going to care that they are “shooting blanks” and that is going to be a big chunk of the population.
The problem wasn’t the lack of children, per se - the problem was the imminent extinction of the human race. Knowing that humanity would be completely and utterly gone in 80 years, max, would probably be a bit of a downer for most people.
But they’ll never have grandchildren, their children will never have families of their own, and humanity is facing extinction which is something that I think would tend to depress even couples with a dozen kids. And it’s got to be really bad for the younger generation knowing that they’re it. There’s nothing to come after them.
One of my all-time favorites. I think the black mood of society as a whole is pretty realistic – it would be very hard to have hope for things to get better if no children were being born.
I thought the scene that really brought it home for me was the empty, decaying school. At first, I was like, “why is it empty?”. (Answer: duh!) Then it hit me.
Schools have always been there, and seeing that they were no longer needed, and nothing was built in their place, really showed how downhill everything was going. No one will EVER play on a swing, learn to read, play with toys, again forever. Which is only going to be about 80 years. It’s one thing to acknowledge that you are going to die; it makes it worse when you know the date.
I thought the wars, and the nuking of NY or whatever (mentioned in passing) might have been too much, but then, I don’t have kids and basically my genetic line ends when I die, so I’m already in the scenario of the movie, and I don’t care. But others would.
Consider the situation of mystery author PD James, who is still a practicing Anglican. Since Britain is already a largely non-religious nation, and is becoming even less Christian over time, she regularly finds herself in churches where the only people in attendance are elderly folks like herself.
Even though the population in Britain is not decreasing drastically, when you’re looking around a church in London on a typical Sunday, it’s easy to IMAGINE that there just aren’t any young people left, that the entire world has grown old.
That’s what inspired her to write the book.
Huh, I never realized either that PD James was a woman, nor that she wrote the book this movie was based on.
Certainly, restaurant meals and airplane flights would become much more pleasant.
(I say this as the parent of a toddler). 
Bear in mind that SOME of the ridiculous things PD James envisioned in an aging, childless world are already HAPPENING in some countries where the birth rate has been plummeting.
In nations like Italy and Japan, older couples have started realizing that they are NEVER likely to have grandchildren.
There’s a big market in Japan for lifelike baby dolls, especially among older women who want to nurture the grandchildren they know they’ll never see.