In critical sociology, age stratification refers to the hierarchical ranking of people into age groups within a society.
Age stratification which is based on an ascribed status is a major source inequality, and thus may lead to ageism.
Some of the advantages of Age Stratification are labour force calculation, estimating dependants, population growth estimation, forming appropriate government policies & planning (e.g. Budgeting more on health care when ageing population is found, increase university capacity to serve increasing numbers of young children) etc.