A basic institution of Kayapó society is the division into age categories, which are socially defined. The most important are meprire for children. At the age of 10 or 12, a boy is taken to the men's house, where he will live until he marries. When he reaches puberty he is initiated and receives his menõrõnu age-category name. After the birth of his first son, a man becomes a member of the mekrare age-category of married persons with children. This is a very important moment in a man's life, marked by a ritual. Upon reaching old age, a man is called mebenget. Before women have children they are kurerere and afterwards mekrare. On certain occasions, age groups are defined in a more visible way, as for instance during their treks, when each age category devotes itself to specific activities, or during certain rituals. Among the Cateté Xikrin, for example, moieties consisting of young bachelors, on the one hand and married men, on the other, carry out various economic, political, and ceremonial activities.
It is only at certain times and places that age categories are emphasized in men's and women's societies. Among the Xingu Kayapó, when a man's first son is born, he must join a men's society. The Kayapo say that they choose the society of their friends. Women join a society corresponding to that of their husband. Among the Mekranoti, for example, there are now two societies. In the past, several societies existed at the same time. Sometimes there are none. Each society has its chief. Sometimes men's societies become very strong political factions, which leads to violent conflict. They often break up, and alliances are redefined. This institution is less apparent among the Xikrin who organize themselves according to age categories.
Conflict. In the formation of a Kayapó man, value is placed on being strong, resistant, and fierce. Young men's scarification and wasp trials during initiation are tests of strength. War traditionally had a leading place in male initiation. Those that had been able to kill an enemy received special tatoo marks. It is obligatory for a man to avenge the deaths of his close relatives.