Adult development encompasses the changes that occur in biological and psychological domains of human life from the end of adolescence until the end of one's life. These changes may be gradual or rapid, and can reflect positive, negative, or no change from previous levels of functioning. Changes occur at the cellular level and are partially explained by biological theories of adult development and aging. Biological changes influence psychological and interpersonal/social developmental changes, which are often described by stage theories of human development. Stage theories typically focus on “age-appropriate” developmental tasks to be achieved at each stage. Erik Erikson and Carl Jung proposed stage theories of human development that encompass the entire life span, and emphasized the potential for positive change very late in life. The concept of adulthood has legal and socio-cultural definitions. The legal definition of an adult is a person who has reached the age at which they are considered responsible for their own actions, and therefore legally accountable for them. This is referred to as the age of majority, which is age 18 in most cultures, although there is variation from 16 to 21. The socio-cultural definition of being an adult is based on what a culture normatively views as being the required criteria for adulthood, which in turn influences the life of individuals within that culture. This may or may not coincide with the legal definition. Current views on adult development in late life focus on the concept of successful aging, defined as “...low probability of disease and disease-related disability, high cognitive and physical functional capacity, and active engagement with life.” Biomedical theories hold that one can age successfully by caring for physical health and minimizing loss in function, whereas psychosocial theories posit that capitalizing upon social and cognitive resources, such as a positive attitude or social support from neighbors and friends, is key to aging successfully. Jeanne Louise Calment exemplifies successful aging as the longest living person, dying at the age of 122 years. Her long life can be attributed to her genetics (both parents lived into their 80s) and her active lifestyle and optimistic[ attitude. She enjoyed many hobbies and physical activities and believed that laughter contributed to her longevity. She poured olive oil on all of her food and skin, which she believed also contributed to her long life and youthful appearance.