Adulthood is the longest stage and normally lasts from age 18 through old age. While there might be smaller psychological or culturally defined stages, adulthood is when human beings are fully grown and must provide entirely for themselves using the skills they learned throughout the first life stages. This is also a significant time because it is when the life cycle is initiated again by the conception and birth of the adult's own children. At the end of the adult life cycle, the body begins to deteriorate and the life cycle eventually ends in death.