How old was Solomon when he became a king?
Solomon was born to King David and Bathsheba in 990 BCE in Jerusalem, he began his reign over Israel from 970–931 BCE the year of his death.
He was 20 years old when he began his reign and was 59 years old when he died, making his reign over Israel 39 years.
His principle wife Naamah who was a foreigner and the mother of Solomons heir Rehoboam, according to both 1 Kings 14:21-31, and 2 Chronicles 12:13
She was an Ammonite, and the only one of all the Queens of Israel or Judah who was a foreigner.
She was the only one of Solomon's 700 wives, who were all of royal birth including his 300 concubines to be mentioned in the Bible, as having borne a child.