from thirty to fifty years old, counting everyone who comes to serve in the work at the Tent of Meeting.
KJV
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.
ASV
from thirty years old and upward until fifty years old shalt thou number them; all that enter in to wait upon the service, to do the work in the tent of meeting.