Numbers 4:24 (KJV)

Take also the sum of the sons of Gershon, throughout the houses of their fathers, by their families;

From thirty years old and upward until fifty years old shalt thou number them; all that enter in to perform the service, to do the work in the tabernacle of the congregation.

This is the service of the families of the Gershonites, to serve, and for burdens:

And they shall bear the curtains of the tabernacle, and the tabernacle of the congregation, his covering, and the covering of the badgers’ skins that is above upon it, and the hanging for the door of the tabernacle of the congregation,

And the hangings of the court, and the hanging for the door of the gate of the court, which is by the tabernacle and by the altar round about, and their cords, and all the instruments of their service, and all that is made for them: so shall they serve.