(I didn't see any rules against purely text posts to stimulate discussion. But if this is against the rules, please let me know)
Some discussion if you're unaware.
...conclude that “shifting priorities” about family, careers, and how to allocate one’s time and resources is the most likely explanation for the dramatic reduction in rates of childbearing seen among more recent cohorts of young adults. We have not found compelling data support for more readily observed (and potentially altered) policy or economic factors, like the price of childcare or rent.
So, is this a problem to you at all? If it is, then how would you address it? If it isn't, is this a problem that can be addressed along with addressing what you believe is the greater problem? How?
It isn't over it's capacity but I also don't think declining birthrates should be considered a problem unless the total amount of people begins to decline at a significant rate. Birthrates only need to be high so that capitalist will have more people from which they can extract capital. If the population stagnates it's not possible for a business to expand indefinitely and investors do not like when they can't profit.
I'm sure there is much more that can be expanded on here but this is a personal belief I just considered and wrote on the spot.
Edit: having young people is important to a communist society as well and a age distribution with a fat middle can be a problem there too because young people do the majority of the work but i think with current technological advances this issue may be and become less significant with time.