Numbers 8:23 YLT

²¹  And the Levites cleanse themselves, and wash their garments, and Aaron waveth them a wave-offering before Jehovah, and Aaron maketh atonement for them to cleanse them,

²²  and afterwards have the Levites gone in to do their service in the tent of meeting, before Aaron and before his sons; as Jehovah hath commanded Moses concerning the Levites, so they have done to them.

²³  And Jehovah speaketh unto Moses, saying,

²⁴  'This 'is' that which 'is' the Levites': from a son of five and twenty years and upward he doth go in to serve the host in the service of the tent of meeting,

²⁵  and from a son of fifty years he doth return from the host of the service, and doth not serve any more,