2 Chronicles 31:16
except those enrolled by genealogy, males from three years old and upward--all who entered the house of the LORDas the duty of each day required--for their service according to their offices, by their divisions.
Ezra 3:4
And they kept the Feast of Booths, as it is written, and offered the daily burnt offerings by number according to the rule, as each day required,
Leviticus 21:22-23
He may eat the bread of his God, both of the most holy and of the holy things,
1 Chronicles 23:3
The Levites, thirty years old and upward, were numbered, and the total was 38,000 men.