Middle age refers to an arbitrary period in a person's life between early adulthood and old age. In industrial societies, such as the United States and Canada, this period now usually extends from about the age of 40 to 65. However, there is no noticeable change in physical or behavioral functioning at either of these ages. The range of middle age may vary in different societies. For example, in nonindustrialized countries, people may be considered old by the age of 40.