Numbers 4:3

From thirty years old and upward until fifty years old shalt thou number them; all that enter in to perform the service, to do the work in the tabernacle of the congregation.

And Jesus himself began to be about thirty years of age, being (as was supposed) the son of Joseph, which was the son of Heli,

Their brethren also the Levites were appointed unto all manner of service of the tabernacle of the house of God.

From thirty years old and upward even unto fifty years old, every one that entereth into the service, for the work in the tabernacle of the congregation:

Seemeth it but a small thing unto you, that the God of Israel hath separated you from the congregation of Israel, to bring you near to himself to do the service of the tabernacle of the LORD, and to stand before the congregation to minister unto them?

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.

This is a true saying, If a man desire the office of a bishop, he desireth a good work.

Not a novice, lest being lifted up with pride he fall into the condemnation of the devil.

From thirty years old and upward even unto fifty years old shalt thou number them, every one that entereth into the service, to do the work of the tabernacle of the congregation.

And Joseph was thirty years old when he stood before Pharaoh king of Egypt. And Joseph went out from the presence of Pharaoh, and went throughout all the land of Egypt.

This charge I commit unto thee, son Timothy, according to the prophecies which went before on thee, that thou by them mightest war a good warfare;