Adult is a term used to describe a human who has transcended teenage years and early adulthood and is therefore considered fully grown or developed. Adults are often characterized as having reached a higher level of maturity, independence, responsibility, and wisdom relative to children or teenagers, though there are plenty of exceptions. Adults are further classified into three major age groups: young adults, middle age, and the elderly. Middle age occurs roughly between the ages of 45 and 65 years old and oftentimes coincides with what is commonly known as a midlife crisis.