Just listened to a radio documentary about Japan's aging population, and the reasons behind it, so had a bunch of thoughts regarding that.
However, before I start, I'd just like to note that this isn't the "fault" of any individual or couple. There has been a thing in the past where the state moralises having children (Lie back and think of England, various dictators, uh... Others), which I guess is a way of trying to solve the problem albeit a heavy handed and kind of sleazy one.
This isn't really about Japan, but generally first world countries with aging populations. Arguably, Japan has one of the worst and certainly most public cases. So, let's go to work. Metaphorically.
Aging Population, bad.:
So, in a way, an aging population is usually indicative of the country having a very good run. However, having an aging population means a bunch of things economically and politically. Namely, aging populations typically have very high pension and medical costs associated with keeping old people around, and those old people provide a very powerful and overly conservative voting bloc. Retirees are not productive. They were, but they're not now. This may or may not be a problem for you, but it's also important to note that any solutions implemented will pay dividends perhaps a generation down the track, well outside the concerns of our standard four to six year election cycles in the West.
However, coming from the opposite end, having a large population of drooling idiots (babies) is also very costly. Schools, lost productivity, daycare, specialty products and so on make having a high proportion of under-working-age children in the population a rather costly endeavour. Of course, if the whole state and population are in agreement to make that sacrifice (rare), then they can go ahead and do that. But they should also be prepared for a lot of negative side effects of a stagnant economy.
So, one wants to have a balance. Enough new working age citizens in proportion to the non-working-age citizens. BUT HOW!?
Immigration vs Birthrate:
It's fairly obvious to anyone with an internet connection or at least two friends that some people have a problem with immigration. Some say this is "subtle" racism, since they don't care about the Anglosphere immigrating about, but let's just take the statement at face value.
Immigration is cheaper than having children. Particularly skilled immigration, people with degrees and capital. Some people may or may not have a problem with that (I'm sure some do), but for the continuation of the state and as an economic boost, a large number of skilled immigrants is very effective; see the USA during and after the Second World War. Certainly, other than language barriers, skilled immigrants can get to work almost immediately after arriving, unlike babies, who can't even make sandwiches. Not in this economy.
However, this is ultimately reliant on how attractive your country is to skilled immigration, which is something you (as citizen Prime) cannot guarantee. Political instability, resource economics, speculative bubbles, and I'm sure many other things outside of a state's control (however much they try) affect how attractive a country is.
So a country should at least have a steady birthrate that promotes at least population maintenance, if not growth.
Of course, how sustainable an amount of growth is is up for debate. Only the most die-hard environmentalists would suggest an active culling of the human population, but many do advocate a lowering of birthrates. The countries with the highest birthrates are not what we're talking about, but on a global scale it is a valid point.
For the purposes of this discussion, I'm going to be using a rough ideal figure of 2.5 children per couple, partly for the old joke about the nuclear family, but also for 2 people per couple plus change for population shock (wars, natural disasters, mass emigration, the plague). This isn't advocating demonising people who have no babies or few babies either (by choice or by inability), but rather about promoting a culture in that roughly that many children is "easy" to have.
Also, I dislike mum culture, but that's just me and has little to do with this.
So, a primary reason for wealthy first world countries having aging populations is that during a generation's most fertile years, there is a massive focus on establishing a career. Even with the historical victories of feminism, there is this perception that taking time out for having children will damage one's career. Enough has been written about that (and this isn't an indictment of feminism, but rather the reactions of work culture around it), so switching tacks.
Personally, I want to get into the games development industry (specifically design). However, there is this fairly pervasive culture that if you're not spending 15 hours a day at the office, especially during crunch time, then you're not being a "team player". While it is an extreme example, such work cultures exist in abundance particularly where worker protection is fairly weak (say, the USA or Japan). The expectation that young people cannot both have a child and work on their careers (due to competition) drops the birthrate during the early stage of adulthood.
A lot of countries have worker protections for parenthood and pregnancy, which is a step in the right direction. Having children shouldn't be in direct competition with career growth, but allowing businesses to entirely make that decision directly results in precisely that.
School and Daycare:
Its educational purpose aside, the K-12 schooling system also functions as a daycare, and a lot of child rearing is done there. It suits the state if schools are a place children want to be; belligerent children are more expensive both down the line as well as immediately in disciplinary costs. The whole school problem especially in impoverished regions of first world countries is not one I would attempt to solve here, but defunding schools and public education is likely not the answer. Part of parenting should be done at home, but it's pretty stupid to reject the idea that schools do not provide at least a part of parenting there. Both need to work in concert as problems from one can bleed into the other, both broadly and culturally, and when just considering the individual.
The standard schooling "day" is shorter than the working day, which means that some focus should also be given to daycare (or some other structure should be used?).
I've noted before that internet culture (as a broad thing, there are smaller cultures within it) is extremely individualistic, even compared to Western culture (again, an overarching culture, just go with it). This fairly obviously reduces childbirth rates as you don't owe your child anything, any expectation otherwise is "entitlement" on the part of the child. People just find it simpler not to have children.
Obviously, this is well outside a state's control, and cultural changes are fairly slow to begin with, so let's move on.
Raising a child from birth costs a lot of money. More than MANY cars. Again, this doesn't stop all parents, but it stops a decent number. The state should subsidise the childcare costs, especially as digital methods of achieving intimacy become more prevalent. Indeed, one could envision where all costs of childcare (within reason) would be covered by the state. However, such a subsidy should have diminishing returns, such that the cost "evens out" around 2.5 children. This is a fairly less hamfisted method of population growth management than China's one child policy.
Talked about this above, but in Japan the combination of rising feminine equality and the existing "family" culture and work culture all clash to conspire to reduce the birthrate significantly. Personally, I agree with Feminism's goals, but its sudden (comparatively) rise next to the fairly stable ideas of a family unit have reduced birthrates. Again, this is a cultural thing and not something the state can influence directly, but by limiting a worker's participation in the workforce (say, to 8 hours a day, 5 days a week), it both benefits the worker and the future of the country a generation down the line, while keeping in line with progressive cultural shifts clashing with older ideas about gender roles in society.
This sort of relates to the individualism above, but specifically an area that the state can encourage (though by no means enforce). It appears in the west we want to live by ourselves. Studio apartments, single family units, and so on all suggest this. However, it is fairly obvious to anyone who's been through the grinder that living with friends is cheaper. Historically, families lived in the same house, thus allowing a child to have more than two "parents", in the sense that not just the biological (or legal) parents raise the child, but the grandparents, aunts, and uncles all help raise the child.
I do wonder if such a situation could work with friends instead of families. Say, three couples in one house, all doing a bit of the housework and picking up slack in child-rearing if, say, one of the parents has a really long work day. This is, of course, the most out there idea I'm proposing in this blog post. Something that would encourage this softly is by addressing tax and welfare on the individual rather than the household, as this would encourage bulk purchasing of groceries and cheaper rent.
Anyway, I write all this out as someone who doesn't really like kids. Apparently I'm passable at babysitting though. That's probably irrelevant.
Also, it would be noted that I talk about the state and the country a lot. Population stability is important for a country, but in subtler ways than direct economic concerns, and typically has a turnaround of one generation or so.