1 Chronicles 23:24-28

These were the sons of Levi according to their fathers’ households, the heads of the fathers’ households of those among them who were counted, in the number of names by their head count, doing the work for the service of the house of the Lord, from twenty years old and upward.

For David said, “The Lord God of Israel has given rest to His people, and He dwells in Jerusalem forever.

Also, the Levites will no longer need to carry the tabernacle and all its utensils for its service.”

For by the last words of David, the sons of Levi were counted from twenty years old and upward.

For their office is to assist the sons of Aaron with the service of the house of the Lord, in the courtyards and in the chambers, and in the purification of all holy things, and the work of the service of the house of God,