The Ageing of the World's Population - United Nations Programme on Ageing

Over the past few years, the world's population has continued on its remarkable transition path from a state of high birth and death rates to one characterized by low birth and death rates. At the heart of that transition has been the growth in the number and proportion of older persons. Such a rapid, large and ubiquitous growth has never been seen in the history of civilization.

The current demographic revolution is predicted to continue well into the coming centuries. Its major features include the following:

One out of every ten persons is now 60 years or above; by 2050, one out of five will be 60 years or older; and by 2150, one out of three persons will be 60 years or older.
The older population itself is ageing. The oldest old (80 years or older) is the fastest growing segment of the older population. They currently make up 13 percent of the 60+ age group and will grow to 20 percent by 2050. The number of centenarians (aged 100 years or older) is projected to increase 14-fold from approximately 265,000 in 2005 to 3.7 million by 2050.
The majority of older persons (55 percent) are women. Among the oldest old, 64 percent are women.
Striking differences exist between regions. One out of five Europeans, but one out of twenty Africans, is 60 years or older.
In some developed countries today, the proportion of older persons is already one in four. During the first half of the 21st century that proportion will be close to one in two in some countries.
As the tempo of ageing in developing countries is more rapid than in developed countries, developing countries will have less time than the developed countries to adapt to the consequences of population ageing.
Based on the latest available information, approximately half of the world’s older population live in urban areas. Thirty years ago, the proportion living in urban areas was about 40 per cent. Large differences exist between more and less developed countries. On average, about 70 percent of older persons in more developed countries, and only 38 percent in the least developed countries are urban dwellers.
Over the last half of the 20th century, 20 years were added to the average lifespan, bringing global life expectancy to its current level of 66 years. Large differences exist between countries, however. In the least developed countries, men reaching age 60 can expect only 15 more years of life and women, 17 more, while in the more developed regions, life expectancy at age 60 is 19 years for men and 23 years for women.
The impact of population ageing is increasingly evident in the old-age dependency ratio, the number of working age persons (age 15 - 64 years) per older person (65 years or older) that is used as an indicator of the 'dependency burden' on potential workers. Between 2005 and 2050, the old-age dependency ratio will almost double in more developed regions and almost triple in less developed regions. The potential socioeconomic impact on society that may result from an increasing old-age dependency ratio is an area of growing research and public debate.