'Thirty' in the Bible

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

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

Three of the thirty chief men went down, and came to David in the harvest time to the cave of Adullam; and the troop of the Philistines was encamped in the valley of Rephaim.

He was more honorable than the thirty, but he didn't attain to the [first] three. David set him over his guard.

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