most legal systems define a specific age for when an individual is allowed or obliged to do particular activities. these age specifications include voting age, drinking age, age of consent, age of majority, age of criminal responsibility, marriageable age, age of candidacy, and mandatory retirement age. admission to a movie for instance, may depend on age according to a motion picture rating system. a bus fare might be discounted for the young or old. each nation, government and non-governmental organisation has different ways of classifying age. in other words, chronological aging may be distinguished from "social aging" (cultural age-expectations of how people should act as they grow older) and "biological aging" (an organism's physical state as it ages).