Free member countries can have a population number between 20 and 25 millions.
If higher, it will decline.
In general, the population in a country will decline if the economic situation is very bad (migration),
if the health care is very very low, (people will die.
Otherwise, in all free member countries, the population will increase very slowly up to 20 to 25 millions.
In full member countries, growth will be much faster, up to a level of about 100 Million.
exception:
In some new countries, the population might be tilted to older groups with smaller numbers in the young groups.
In such a case, older people may die faster than newborns take their place.
Please check the population page.
if this is the case, it may take some time but it will correct itself and growth will return.