Trends in the age structure of a population should be considered in policy development and planning by governments and private businesses, because demands for goods and services, labor force participation rates, health conditions, and people's behavioral patterns vary substantially with age. Age structure is primarily determined by fertility, mortality, and migration during the last several decades. Most developed and developing countries in the world have experienced notable changes in the age structure due to significant declines in fertility and mortality. Various statistical and mathematical tools have been developed for measuring and analyzing age structure trends and their effects.
Horiuchi, S. (2015). Age Structure. In International Encyclopedia of the Social & Behavioral Sciences: Second Edition (pp. 338–343). Elsevier Inc. https://doi.org/10.1016/B978-0-08-097086-8.34030-2