Middle age is the period of age beyond young adulthood but before the onset of old age.
According to the Oxford English Dictionary middle age is between 45 and 65: "The period between early adulthood and old age, usually considered as the years from about 45 to 65." The US Census lists the category middle age from 45 to 65. Merriam-Webster list middle age from 45 to 64, while prominent psychologist Erik Erikson saw it starting a little earlier and defines middle adulthood as between 40 and 65. The Collins English Dictionary, list it between the ages of 40 and 60. and the Diagnostic and Statistical Manual of Mental Disorders - the standard diagnostic manual of the American Psychiatric Association - used to define middle age as 40 to 60, but as of DSM-IV (1994) revised the definition upwards to 45 to 65.
This time in the lifespan is considered to be the developmental stage of those who are between 20 years old and 40 years old. Recent developmental theories have recognized that development occurs across the entire life of a person as they experience changes cognitively, physically, socially, and in personality.
This time period in the life of a person can be referred to as middle age. This time span has been defined as the time between ages 45 to 65 years old. Many changes may occur between young adulthood and this stage. The body may slow down and the middle aged might become more sensitive to diet, substance abuse, stress, and rest. Chronic health problems can become an issue along with disability or disease. Approximately one centimeter of height may be lost per decade. Emotional responses and retrospection vary from person to person. Experiencing a sense of mortality, sadness, or loss is common at this age.
Those in middle adulthood or middle age continue to develop relationships and adapt to the changes in relationships. Changes can be the interacting with growing and grown children and aging parents. Community involvement is fairly typical of this stage of adulthood, as well as continued career development.
Middle-aged adults may begin to show visible signs of aging. This process can be more rapid in women who have osteoporosis. Changes might occur in the nervous system. The ability to perform complex tasks remains intact. Women between 48 and 55 experience menopause, which ends natural fertility. Menopause can have many side effects, some welcome and some not so welcome. Men may also experience physical changes. Changes can occur to skin and other changes may include decline in physical fitness including a reduction in aerobic performance and a decrease in maximal heart rate. These measurements are generalities and people may exhibit these changes at different rates and times.