Country population will probably grow to 100 to 120 millions depending on the welfare and health system in the country. These numbers are much increased from the 50 to 60 millions we had in the past.
in addition, in the past, when you tried to increase you population to much larger numbers, such increase was followed by quite steep reductions that tended to return the population numbers to lower levels.
this was indeed changed, already long ago, to eliminate the steep reductions.
Currently, numbers in the young groups, mainly the birth numbers are kept stable. Birth rates are programmed to decline if the population grows. we have made sure that these numbers stop declining and remain stable even at very high population levels.
despite all this, you do see declines. These declines are the result of natural death but mainly death from health related reasons in all age groups. The decline is much slower than ever before.
The decline can be much reduced if your healthcare is at a very high level. Death numbers can in fact go close to zero. I am not sure you want or can pay for an extreme level health system that will go so far. The numbers of births and deaths in countries with high population can be somewhat distorted due to the corrections in birth numbers at such levels.
we are very interested in detailed observations by players who keep finding situation where the numbers do not match our claims and errors do pop up, several times recently. All these errors were discovered and subsequently corrected, due to in depth reports by players.