'Thirty' in the Bible

David was thirty years old when he began to reign; he reigned forty years.

And David again gathered all the chosen men of Israel, thirty thousand.

And three of the thirty chiefs went down, and came to David in the harvest time to the cave of Adullam, when the troop of the Philistines was encamped in the valley of Rephaim.

He was honoured above the thirty, but he did not attain to the first three. And David set him in his council.

Asahel the brother of Joab was one of the thirty; Elhanan the son of Dodo of Bethlehem,