From a good article on aging, Mine Is Longer Than Yours by Michael Kinsley in The New Yorker, April 2008:
If a hundred Americans start the voyage of life together, on average one of them will have died by the time the group turns sixteen. At forty, their lives are half over: further life expectancy at age forty is 39.9. And at age sixty-three the group starts losing an average of one person every year. Then it accelerates. By age seventy-five, sixty-seven of the original hundred are left. By age one hundred, three remain.