What factors determine a population's size and structure?

Factors like Education, Economic condition of people, Various facilities like airports, hospitals, schools, and many more, social culture, family planning etc

Hope it helps:)

this is a pretty broad question and can be a pretty lengthy answer. since 1900, women have gained a lot more rights and have become active in the workforce. with women being in the workforce, men play a larger role in family life. many family tasks are shared between men and women, whereas, women used to be the sole family caretakers.

that should get you started at least.