Having a large population is not the key to success with your village, although it is important. The population growth rate is a factor in your village’s overall prosperity. With that in mind, it is important to keep your population growing at a steady, sustainable rate. If the population grows too quickly, you may find that you don’t have the agricultural infrastructure present to sustain it.
Another advantage of growing your population is that the percentage of people working to meet the village’s basic needs will decrease, freeing up more workers to concentrate on cash crops. You will also be able to hire more itinerant workers as your population grows. This can become a virtuous circle if you keep investing in the welfare of your people, by reducing the amount they have to do and buying luxury stores at the market.
How does population grow?
Simple - population grows when the birth rate exceeds the death rate! In order to give birth, a woman has to be married and has to be moderately healthy. Happiness is a small factor here -- people won’t get married if they’re miserable, but they don’t have to be ecstatic to get married either.
Once a child has been born, health is again extremely important. The more healthy the mother is, the more likely she will be to survive childbirth, and children themselves are much more likely to survive the first few years of childhood if they are healthy and well fed. A person can die of disease at any time, but they are particularly vulnerable when very young and very old.
So, health is very important in ensuring that the population continues to grow, in terms of parents being able to conceive and children being able to survive into adulthood. Maintaining a large enough adult population is also important -- there needs to be plenty of parents so there can be plenty of children. Keeping the whole population healthy is obviously a factor here, but doing your best to avoid or mitigate the effects of disasters such as floods and bandit attacks is also very important. If you are not careful, these types of events can whittle away your child bearing population, leaving just the young and the old alive.
Working population
Children begin to work at the age of 12, and continue to work until they are 60, if they survive that long! People in this age range won’t work if they are too unhealthy or if they are pregnant, but everyone else should be hard at work in the fields all the time.
You should strive to meet the working proportion of your population as high as possible at all times, especially if you have just had a population boom. It can be easy to get into trouble if you have too many mouths to feed and not enough workers.