Numbers 8:25

And from the age of fifty years they shall cease waiting upon the service thereof, and shall serve no more:

At fifty years old the Levites ceased the arduous, manual, active, toilsome part of waiting upon the sanctuary service, being released from regular active waiting upon its service. They were not discharged altogether, but retained charge of the work without being expected to perform its harder tasks, continuing in official service and sacred duties, still able to wait on God, honor Him, and receive comfort from Him. The fifty-year limit did not limit the priestly office, which continued for life, so a man does not cease to be a priest because he grows old. In the same way a gospel minister does not cease to be a minister when he grows old; aged ministers are still ministers. The verse therefore does not mean an aged minister should lose support; the tithe and offering system was to provide for workers throughout their lives, and the tithe is the proper fund to care for aged ministers.

The verse makes provision for those who have officially served the Lord fifty years. It is like a humane government pensioning its old soldiers. It shows responsibility to look after faithful servants and their dependent families when old age comes upon them, for God never leaves His people because they are old if they have continued faithfully in His service.