1 Chronicles 23:4, 24

Of these, twenty and four thousand were to oversee the work of the house of Jehovah; and six thousand were officers and judges

These were the sons of Levi after their fathers’ houses, even the heads of the fathers’ houses of those of them that were counted, in the number of names by their polls, who did the work for the service of the house of Jehovah, from twenty years old and upward.