TSK · Numbers 4:3

from twenty years old and upward, all who are able to go out to war in Israel. You and Aaron shall number them by their divisions.

They shall keep his requirements, and the requirements of the whole congregation before the Tent of Meeting, to do the service of the tabernacle.

you shall count them from thirty years old and upward even to fifty years old, everyone who enters on the service, to do the work of the Tent of Meeting.

from thirty years old and upward even to fifty years old, everyone who entered in to do the work of service, and the work of bearing burdens in the Tent of Meeting,

Is it a small thing to you, that the God of Israel has separated you from the congregation of Israel, to bring you near to himself, to do the service of the tabernacle of Yahweh, and to stand before the congregation to minister to them;

Their brothers the Levites were appointed for all the service of the tabernacle of the house of God.

These were the sons of Levi after their fathers' houses, even the heads of the fathers' houses of those who were counted individually, in the number of names by their polls, who did the work for the service of the house of Yahweh, from twenty years old and upward.

and the pattern of all that he had by the Spirit, for the courts of the house of Yahweh, and for all the surrounding rooms, for the treasuries of the house of God, and for the treasuries of the dedicated things;

and those who were reckoned by genealogy of the priests by their fathers' houses, and the Levites from twenty years old and upward, in their offices by their divisions;

Jesus himself, when he began to teach, was about thirty years old, being the son (as was supposed) of Joseph, the son of Heli,

Finally, be strong in the Lord, and in the strength of his might.

This is a faithful saying: if a man seeks the office of an overseer, he desires a good work.