A gerontocracy is a form of oligarchical rule in which an entity is ruled by leaders who are significantly older than most of the adult population. In many political structures, power within the ruling class accumulates with age, making the oldest the holders of the most power. Those holding the most power may not be in formal leadership positions, but often dominate those who are. In a simplified definition, a gerontocracy is a society where leadership is reserved for elders.
Although the idea of the elderly holding power exists in many cultures, the gerontocracy has its western roots in ancient Greece. Plato famously stated that "it is for the elder man to rule and for the younger to submit". One example of the ancient Greek gerontocracy can be seen in the city state of Sparta, which was ruled by a Gerousia, a council made up of members who were at least 60 years old and who served for life.