The world's population of older people is growing at the fastest rate ever seen and the old will soon outnumber the young for the first time, U.S. researchers reported on Monday. An aging population will push up pension and healthcare costs, forcing major increases in public spending that could slow economic growth in rich and poor countries. The number of people 65 and older hit about 506 million as of midyear 2008, according to the U.S. Census Bureau. This will double to 1.3 billion by 2040, accounting for 14 percent of the total global population. "People aged 65 and over will soon outnumber children under age 5 for the first time in history," said the report put together by Kevin Kinsella and Wan He of the U.S. Census Bureau and quoted by Reuters.