Why We Love: The Nature and Chemistry of Romantic Love

by Helen Fisher

In 1900, only 4 percent of Americans were over age sixty-five; today II percent survive to this age; by 2030 some 20 percent of all Americans will be over sixty-five; by 2050, 15 to 19 percent of the world population will be over age sixty-five as well.

In fact, some demographers say we should begin to think of middle age as extending to age eighty-five, largely because 40 percent of men and women at that age are fully functional.