That was the work span of the Levites. After age 50, they could support those younger who worked in the tabernacle, but they could not do the work themselves,

Then the Lord spoke to Moses, saying, “This is what pertains to the Levites: From twenty-five years old and above one may enter to perform service in the work of the tabernacle of meeting; and at the age of fifty years they must cease performing this work, and shall work no more. They may minister with their brethren in the tabernacle of meeting, to attend to needs, but they themselves shall do no work. Thus you shall do to the Levites regarding their duties” (Numbers 8.23–26).

Sometimes we say that we are glad not to have been involved in their work, which was the endless slaughter of animals, yet, retiring at 50 sounds pretty good! However, the Lord knew that they would want to continue to have a connection with the great service to the Lord, and so He allowed it, but in a limited way.

Perhaps you cannot do what you used to do, but what you can do in the church, by all means, please keep doing it, for we need as many workers as possible.