Aging Americans will make up an unprecedented proportion of the population as the 78 million baby boomers reach age 50. The baby boomers, those born between 1946 and 1964, will first reach age 65 in 2011, transforming the 35 million people over age 65 in 2000 to an estimated 69 million by 2030. With improved health care, , and health behaviors, people 85 and over are expected to be the fastest-growing group of elderly persons, tripling from 4 million in 2000 to about 14 million by 2040. Growth in the elderly population has led to two subgroups: the young-old (55 to 74 years) and the old-old (75 and older). Still, elderly people remain the most diverse segment of American society.