1 Kings 2:11

The days that David reigned over Israel were forty years: seven years he reigned in Hebron and thirty-three years he reigned in Jerusalem.

David was thirty years old when he became king, and he reigned forty years.

Now David the son of Jesse reigned 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, and he reigned forty years.

Now David the son of Jesse reigned over all Israel.