The world population has been classified into three age groups: 

1. 0 – 14 years 

2. 15 – 64 years 

3. 65 years and above.

1. 0 – 14 years age groups: 35 per cent of world population is included in this age group. There are differences in this age group in different regions of the world. In developed countries, 18.3 per cent of total population is included in this group, while in developing countries, this per centage rises up by 32.2. In countries where birth rate is high, the population of this age group is in surplus. Generally, population of this group is dependent.

2. 15 – 64 years age group: The young or the adult population is included in this group. This population is more than any other group. This population is more productive, creative and dynamic. Development of a country depends upon this group. This is the working population.

3. 65 years and above: Population related to this group is called the elderly group. Old population is found in those types of countries where all demographic transition stages had been completed much earlier.