TSK · Numbers 4:35

you shall count them from thirty years old and upward until fifty years old; all who enter in to wait on the service, to do the work in the Tent of Meeting.

from thirty years old and upward even to fifty years old, everyone who entered into the service, for work in 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,

The Levites were numbered from thirty years old and upward: and their number by their polls, man by man, was thirty-eight thousand.

Also the Levites will no longer need to carry the tabernacle and all its vessels for its service."

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