The Elgeiyo social organisation centres on the age set, or . There are eight age-sets () which are rotational, meaning after the end of one age set (after approximately 120 years), new members of age-set are born. Unlike the Nandi and the Tugen who have only seven age sets (due to loss of an entire age set in battle), the Keiyo retained all the eight age sets. The order is given below. was given out during initiation. The age set system is organized in such a way that a father and a son cannot be of the same or sequential age sets. That is, there ought to be one between a father and a son. For example, a Kipkoimet cannot beget a Kaplelach. The Elgeiyo do not consider a woman to have an age set, hence she can marry any age set except that in which her father belongs.