“This is the rule the Levites must follow: They must begin serving in the Tabernacle at the age of twenty-five, 25 and they must retire at the age of fifty. After retirement they may assist their fellow Levites by serving as guards at the Tabernacle, but they may not officiate in the service. This is how you must assign duties to the Levites.” - Numbers 8:24-26 NLT