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.
