The population
age structure and the pattern of changes in it differ greatly among major regions
of the world. Children under the age of 15 made up only 22 per cent of total population in the
developed regions in 1985, but 37 per cent in the developing regions (including China); 45 per cent
in Africa. The elderly population (aged 60 years and older) comprised 16 per cent of the total
population of the developed regions, but only 7 per cent in the developing regions; in Africa they
comprised only 5 per cent, in the middle range of the age distribution, the developed regions had a
relatively small proportion (16 per cent) of youth aged 15 to 24, and a relatively large proportion
of adults aged 25 to 59 46 per cent). Youth comprised 20 per cent of the total population n the
developing regions, while those in the 25 to 59- year-old group were only 36 per cent of the total.
Changes in fertility
and mortality in the past 50 years have introduced bulges and troughs in the
age structure, with predictable time lags. Especially noteworthy are the baby booms that occurred
shortly after the Second World War in many developed countries, and the drop of fertility rates
with varying speed and timing among many developed countries in the past 50 years. Significant
reductions of infant and child mortality rates, or increases in fertility rates, resulted in a sharp
increase in the child and school-age populations during the 1950s and 1960s. Forty to fifty per
cent of the world's population increase in those decades consisted of children under 15 years of
age. With a time lag, these inflated population cohorts moved to the youth category. As they
reached adulthood, the main working-age population, aged 25 to 59, began to increase rapidly in
the 1980s and will continue to accelerate into the 21st century.
The primary and
secondary school-age populations are defined by the United Nations
Educational, Scientific and Cultural Organization (UNESCO) for statistical purposes as children
aged 6 to 11, and 12 to 17, respectively. In the developed countries plus China and several other
countries in East Asia, the school-age population declined in the 1980s as a result of the fertility
decline in the 1970s. As a result of the gradual fertility decline the school-age population in Latin
America and southern Asia increased more slowly in the 1990s than before. In Africa, however,
it continued to grow rapidly, at about the same rate as the total population.
