3,912. Age Limits and Duty Rosters

Hilchos Klei HaMikdash 3:8

Numbers 8:25 teaches “At the age of 50, he (the Levi) will return from the service of the work (of the Tabernacle).” This only applied when the Mishkan was carried from place to place; it was not a permanent mitzvah intended for future generations. In the Temple, a Levi isn’t disqualified because of age or physical imperfections; he is only disqualified if his voice deteriorates because of his age. The Rambam opines that such a Levi is only disqualified from singing, but he could still serve as a gatekeeper.

Hilchos Klei HaMikdash 3:9

The prophet Samuel and King David divided the Leviim into 24 watches, a different one of which would serve each week in the Temple. The leader of each watch would subdivide his crew into families. Every day, the designated members would serve and the heads of the families would assign to them their various responsibilities. The Leviim were warned not to perform the altar service, as per Numbers 18:3: “To the holy vessels and the altar they shall not draw near so they will not die.” From this we see that they may not draw near to the Temple service, but they may touch the service vessels.