2 Chronicles 31:16
besides those who were reckoned by genealogy of males, from three years old and upward, even everyone who entered into the house of Yahweh, as the duty of every day required, for their service in their offices according to their divisions;
Ezra 3:4
They kept the feast of tents, as it is written, and [offered] the daily burnt offerings by number, according to the ordinance, as the duty of every day required;
Leviticus 21:22-23
He shall eat the bread of his God, both of the most holy, and of the holy.
1 Chronicles 23:3
The Levites were numbered from thirty years old and upward: and their number by their polls, man by man, was thirty-eight thousand.