Old age has historically been measured by chronological age. However, this metric does not take into account improvements in life expectancy and health, says Futurity. In 1800, a European male had only a 25 percent chance of reaching the age of 60, whereas 90 percent of contemporary European men do.
Old age is perceived differently as people age themselves, says Forbes magazine. As the current generation grows older, they adjust their definition of "old" upward. Women, who have a greater life expectancy than men, are less apt to call a 63-year-old person old. A Marist College poll shows that the age someone considers old rises correspondingly with the age of the survey participant.
The definition of old age is important because of the increasing number of people in developed countries who may or should be eligible for retirement benefits. By 2050, 22 percent of the world's population will be over 60, and the number of people 80 years and older will quadruple according to the World Health Organization.
Low and middle-income nations, such as Brazil and China, will experience the fastest rate of demographic change. Even in less-developed countries, more people die of lifestyle-related factors, such as heart disease, cancer and diabetes, than from communicable disease. The rate of aging and gradual decline depends on diet, exercise and exposure to health risks, such as tobacco or alcohol, says the World Health Organization.