Ageing or aging is the process of systems' deterioration with time. This article focuses on the social, cognitive, cultural, and economic effects of ageing. The biology of ageing is treated in detail in senescence. Ageing is an important part of all human societies reflecting the biological changes that occur, but also reflecting cultural and societal conventions. Age is usually measured in full years (except for young children, where this downward rounding would be too crude) and a person's birthday is often an important event.
The issue of an ageing population, where the average age of a society is higher now due to higher standards of living is increasingly important in many nations of the world. The societal effects of age are great. Young people tend to commit most crimes, they are more likely to push for political and social change, to develop and adopt new technologies, and to need education. Older people have different requirements from society and government as opposed to young people, and frequently differing values as well. Older people are also far more likely to vote, and in many countries the young are forbidden from voting, and thus the aged have comparatively more political influence.