the delimma of the population mechanics is, there is either complete acceleration or complete deceleration there is nothing constant.
lets take an example of india, it is not decelerating, This is resulting in india overtaking china in few years or decades, while china will be a lot less populated than india in next few decades.
i have been to UK and some results of population mechanics are shocking, in a particular city when i roamed in the afternoon, i was shocked to see buses filled with oldies, not one young person was present. in complete contrast to pakistan where mostly the commuters are young men and women, not many oldies.
While decelerating population, the resources are much better distributed, but there the nation faces dilemma of old people overcoming younger generation.
regards