2 Chronicles 31:17

as well as the priests who were enrolled genealogically according to their fathers’ households, and the Levites from twenty years old and upwards, by their duties and their divisions.

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.

1 Chronicles 23:27

For by the last words of David the sons of Levi were numbered from twenty years old and upward.

Numbers 3:15

Number the sons of Levi by their fathers’ households, by their families; every male from a month old and upward you shall number.”

Numbers 3:20

and the sons of Merari by their families: Mahli and Mushi. These are the families of the Levites according to their fathers’ households.

Numbers 4:3

from thirty years and upward, even to fifty years old, all who enter the service to do the work in the tent of meeting.

Numbers 4:38

The numbered men of the sons of Gershon by their families and by their fathers’ households,

Numbers 4:42

The numbered men of the families of the sons of Merari by their families, by their fathers’ households,

Numbers 4:46

All the numbered men of the Levites, whom Moses and Aaron and the leaders of Israel numbered, by their families and by their fathers’ households,

Numbers 8:24

“This is what applies to the Levites: from twenty-five years old and upward they shall enter to perform service in the work of the tent of meeting.

Numbers 17:2-3

“Speak to the sons of Israel, and get from them a rod for each father’s household: twelve rods, from all their leaders according to their fathers’ households. You shall write each name on his rod,

1 Chronicles 24:20-26

Now for the rest of the sons of Levi: of the sons of Amram, Shubael; of the sons of Shubael, Jehdeiah.

2 Chronicles 31:2

And Hezekiah appointed the divisions of the priests and the Levites by their divisions, each according to his service, both the priests and the Levites, for burnt offerings and for peace offerings, to minister and to give thanks and to praise in the gates of the camp of the Lord.

Ezra 2:59

Now these are those who came up from Tel-melah, Tel-harsha, Cherub, Addan and Immer, but they were not able to give evidence of their fathers’ households and their descendants, whether they were of Israel:

Treasury of Scripture Knowledge

Summary

Both to the genealogy of the priests by the house of their fathers, and the Levites from twenty years old and upward, in their charges by their courses;

Bible References

Genealogy

Numbers 3:15
Number the sons of Levi by their fathers’ households, by their families; every male from a month old and upward you shall number.”
Numbers 4:38
The numbered men of the sons of Gershon by their families and by their fathers’ households,
Numbers 17:2
“Speak to the sons of Israel, and get from them a rod for each father’s household: twelve rods, from all their leaders according to their fathers’ households. You shall write each name on his rod,
Ezra 2:59
Now these are those who came up from Tel-melah, Tel-harsha, Cherub, Addan and Immer, but they were not able to give evidence of their fathers’ households and their descendants, whether they were of Israel:

Twenty

Numbers 4:3
from thirty years and upward, even to fifty years old, all who enter the service to do the work in the tent of meeting.
Numbers 8:24
“This is what applies to the Levites: from twenty-five years old and upward they shall enter to perform service in the work of 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.

By their courses

2 Chronicles 31:2
And Hezekiah appointed the divisions of the priests and the Levites by their divisions, each according to his service, both the priests and the Levites, for burnt offerings and for peace offerings, to minister and to give thanks and to praise in the gates of the camp of the Lord.
1 Chronicles 24:20
Now for the rest of the sons of Levi: of the sons of Amram, Shubael; of the sons of Shubael, Jehdeiah.