Treasury of Scripture Knowledge
Now in the second year of their coming unto the house of God at Jerusalem, in the second month, began Zerubbabel the son of Shealtiel, and Jeshua the son of Jozadak, and the remnant of their brethren the priests and the Levites, and all they that were come out of the captivity unto Jerusalem; and appointed the Levites, from twenty years old and upward, to set forward the work of the house of the LORD.
Twenty years old
thirty years and upward, even to fifty years old, all who enter the service to do the work in the tent of meeting.
1 Chronicles 23:24
These were the sons of Levi according to their fathers’ households, even the heads of the fathers’ households of those of them who were counted, in the number of names by their census, doing the work for the service of the house of the Lord, from twenty years old and upward.