In 2005, 10% of the population was over the age of 60. In the developing world this was 8% of the population, and in the developed world 20%. This proportion is expected to increase to 20% by 2050.
In 2005, 670 million people were aged 60 years and over. This is projected to increase to 1 billion by 2020 and to 2 billion by 2050.
Causes increased life expectancy and the decline in fertility.
Although ageing of the population has begun later in the less economically developed world, it is progressing at a faster rate than in the developed world. This is because the relative rates of decline in both fertility and mortality are much greater in developing than in developed countries.
The global average for life expectancy increased from 46 years in 1950 to 64 in 2000. It is projected to reach 74 years by 2050.
During the same time period, the proportion of children is projected to fall from 33% to 20%.
The population aged 80 and over numbered 72 million in 2005. This is the fastest-growing section (4.2% annually) of global population and is projected to increase to 394 million by 2050.
Europe is the 'oldest' region in the world. Those aged 60 and over in 2000 formed 20% of the population and this is projected to rise to 35% by 2050.
The % of old people and their rate of increase varies among countries. In 2005, those aged 60 and over ranged from + 25% in Japan, Italy and Germany to less than 5% in most tropical African countries and in the oilrich countries of the middle east that attract young worker. By 2050, the range is expected to be even wider, from more than 40% in Japan, Slovenia and N. Korea to even less than 5% in the African countries of Swaziland and Liberia.
By 2025, more than a third of the UK's population will be over 55. We're living longer and staying active until much later in life. So why the pessimism about the rise of Britain's ageing population?
The underlying cause is that we are living longer and having fewer children - well below the replacement rate of 2.2 per woman - but the size of the baby boomer generation, who are just starting to retire, is accelerating the trend.
By 2014, projections suggest, over-65-year-olds will overtake the under-16s.
And by 2025, the number of over-60s will have passed the under-25s for the first time.
Life expectancy at birth is increasing but an even more telling figure is the increase in life expectancy after 60.
In the UK, a man who turned 60 in 1981 could expect to live another 16 years and a woman almost 21 years.
By 2003 this had increased to 20 years for men and 23 for women; and according to official UK projections, by 2026 this will rise to almost 24 years for men and almost 27 for women.