However, these countries do have the largest number of older people, 109 million and 62 million, respectively. Both countries are projected to undergo more rapid ageing, and by 2050, will have about 350 million and 240 million people 65 and older, respectively, the US census Bureau said. From 2009 to 2050, the world's 85 and older population is projected to increase more than fivefold, from 40 million to 219 million. Because women generally live longer than men, they account for slightly more than half of the older population and represent nearly two-thirds of the 85 and older population.

Europe likely will continue to be the oldest region in the world: by 2050, 29 per cent of its total population is projected to be 65 and older. On the other hand, sub-Saharan Africa is expected to remain the youngest region as a result

of relatively higher fertility and, in some nations, the impact of HIV/AIDS.

Only 5 per cent of Africa's population is projected to be 65 and older in 2050, the report said.

Countries experiencing relatively rapid declines in fertility combined with longer life spans will face increasingly older populations. These countries will see the highest growth rates in their older populations over the next 40 years, it said.