Numbers 8:23-26 - Retirement Of The Levites
23 Then the Lord spoke to Moses: 24 "This is what pertains to the Levites: At the age of twenty-five years and upward one may begin to join the company in the work of the tent of meeting, 25 and at the age of fifty years they must retire from performing the work and may no longer work. 26 They may assist their colleagues in the tent of meeting, to attend to needs, but they must do no work. This is the way you must establish the Levites regarding their duties."