What is the impact of development on age structure of the population?

Smaller proportions of the population are found in the younger age groups (i.e. 0-4 years, 05 to 09 years and 10 to 19 years) and larger proportions in the older age groups (i.e. 60-64, 65-69, 70-74, 75-79 and 80 + years).