The marks of old age are so unlike the marks of middle age that legal scholar Richard Posner suggests that, as an individual transitions into old age, he/she can be thought of as different persons "time-sharing" the same identity. Gillick, a baby boomer, accuses her contemporaries of believing that by proper exercise and diet they can avoid the scourges of old age and proceed from middle age to death.
In addition to chronological age, people can be considered old because of the other dimensions of old age.
For example, people may be considered old when they become grandparents or when they begin to do less or different work in retirement.
The AARP allows couples in which one spouse has reached the age of 50 to join, regardless of the age of the other spouse.
The distinguishing characteristics of old age are both physical and mental.
The age which qualifies for senior citizen status varies widely.