Numbers 8:23

²¹So the Levites purified themselves and washed their garments; and Aaron presented them as a gift before the Lord, and Aaron made atonement for them to purify them.

²²And afterward the Levites went in to minister in their service in the tabernacle of witness before Aaron, and before his sons; as the Lord appointed Moses concerning the Levites, so they did to them.

— Numbers 8:23 —

²⁴This is the ordinance for the Levites; From five and twenty years old and upward, they shall go in to minister in the tabernacle of witness.

²⁵And from fifty years old the Levite shall cease from the ministry, and shall not work any longer.