1 Kings 2:11

He was king of Israel for forty years. He ruled seven years in Hebron and thirty-three years in Jerusalem.

David was thirty years old when he became king. He ruled for forty years.

David son of Jesse ruled over all Israel

Treasury of Scripture Knowledge

And the days that David reigned over Israel were forty years: seven years reigned he in Hebron, and thirty and three years reigned he in Jerusalem.

David was thirty years old when he became king. He ruled for forty years.

David son of Jesse ruled over all Israel