Numbers 4:37-39

King James Version

³⁷ These were they that were numbered of the families of the Kohathites, all that might do service in the tabernacle of the congregation, which Moses and Aaron did number according to the commandment of the Lord by the hand of Moses.

³⁸ And those that were numbered of the sons of Gershon, throughout their families, and by the house of their fathers,

³⁹ From thirty years old and upward even unto fifty years old, every one that entereth into the service, for the work in the tabernacle of the congregation,