'Twenty' in the Bible

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.

For by the last words of David, the Levites from twenty years old and above were counted.

But David did not count those twenty years of age and under, for the Lord had said he would multiply Israel as the stars of heaven.