The NIV Bible translation of 2 Kings 14:9 is the following:
"But Jehoash king of Israel replied to Amaziah king of Judah: "A thistle in Lebanon sent a message to a cedar in Lebanon, 'Give your daughter to my son in marriage.' Then a wild beast in Lebanon came along and trampled the thistle underfoot."
The commentary from the NIV Study Bible describes this verse as follows:
"Jehoash king of Israel replied to Amaziah in the form of a fable - a kind of a story designed to teach a moral. By speaking of Amaziah as a thistle in comparison with the cedar of Lebanon, Jehoash tried to help Amaziah put a more realistic construction on his recent victory."
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He was 7 years old.
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2 Kings 11:21: "Seven years old [was] Jehoash when he began to
reign." It appears that Joash and Jehoash were one and the same
person. He became the King of Judah and reigned for 40 years, doing
that which was good in the sight of the Lord. In fact he was one of
the best kings to ever reign. I believe there was a king of Israel
with the same name who ruled in Samaria a little further in the
history of the Kings of Judah and Israel. These two states were
separate kingdoms and had separate kings and were normal feuding
with each other. From the verse above you can read the whole
story>