We review research findings on the oldest old that demonstrate that the fourth age entails a level of biocultural incompleteness, vulnerability and unpredictability that is distinct from the positive views of the third age (young old). The oldest old are at the limits of their functional capacity and science and social policy are constrained in… Continue reading New Frontiers in the Future of Aging: From Successful Aging of the Young Old to the Dilemmas of the Fourth Age