These were the Levites by their fathers’ households, the heads of the fathers’ households of those registered, according to the number of names of the individuals who were the servants of the house of the Lord, from twenty years old and upward.
the plan for the divisions of the priests and the Levites and for all the work of the service in the house of the Lord and for all the utensils for service in the house of the Lord;
from thirty years and upward to fifty years old, you shall number them, everyone who enters the service to do the work of the Tent of Meeting (tabernacle).
from thirty years and upward even to fifty years old, everyone who could enter to do the work of service and the work of carrying in the Tent of Meeting (tabernacle);
and He must not be a new convert, so that he will not [behave stupidly and] become conceited [by appointment to this high office] and fall into the [same] condemnation incurred by the devil [for his arrogance and pride]. [Is 14:12-14]