Old age Main article: Old age The World Health Organization finds "no general agreement on the age at which a person becomes old." Most "developed countries" set the age as 60 or 65. However, in developing countries inability to make "active contribution" to society, not chronological age, marks the beginning of old age. [80] According to Erikson's stages of psychosocial development , old age is the stage in which individuals assess the quality of their lives. In reflecting on their lives, people in this age group develop a feeling of integrity if deciding that their lives were successful or a feeling of despair if evaluation of one's life indicates a failure to achieve goals. [81] Physically, older people experience a decline in muscular strength, reaction time, stamina, hearing, distance perception, and the sense of smell. [82] They also are more susceptible to diseases such as cancer and pneumonia due to a weakened immune syst...