According Kalenjin social system, the male sex is divided into boys, warriors and elders. The female sex is divided into girls and married women. The first stage began at birth and continued till initiation.
All boys who were circumcised together are said to belong to the same ibinda or ipinda. These age sets played a significant role in traditional Kalenjin society since they were used to record time. Once the young men of a particular ibinda came of age, they were tasked with protecting the tribal lands and the society, the period when they were in charge of protection of the society was known as the age of that ibinda. There were eight ages in general though this varied between sections as an age-set would temporarily be dropped from use if a disastrous incident occurred during the age of the ibinda.
Historically, the Nandi had eight cyclical age-sets or ibinwek, however they dropped one for a total of seven. Legend has it that the members of this ibinda were wiped out in war. For fear of a recurrence, the community decided to retire the age-set.
The order of Nandi ibinwek is roughly as given below.
In each age-set, the initiates were bundled into siritiet or what can be understood as a 'team'. There are four 'teams' or siritoik in an ibinda namely: