מִבֶּ֨ן שְׁלֹשִׁ֤ים שָׁנָה֙ וָמַ֔עְלָה וְעַ֖ד בֶּן־חֲמִשִּׁ֣ים שָׁנָ֑ה כָּל־בָּא֙ לַצָּבָ֔א לַעֲשׂ֥וֹת מְלָאכָ֖ה בְּאֹ֥הֶל מוֹעֵֽד׃
from thirty years old and upward even until fifty years old, all that enter upon the service, to do work in the tent of meeting.
On Flight and Finding
[37] It was on this principle too that the Levites were charged to perform their active service until the age of fifty (Numb. 4:3 ff.), but, when released from their practical ministry, to make everything an object of observation and contemplation; receiving as a prize for duty well done in the active life a quite different way of life whose delight is in knowledge and study of principles alone.