Charles Spurgeon Commentary 2 Chronicles 24:1

"Joash was seven years old when he began to reign; and he reigned forty years in Jerusalem: and his mother`s name was Zibiah, of Beer-sheba." — 2 Chronicles 24:1 (ASV)

Joash was seven years old when he began to reign, and he reigned forty years in Jerusalem.

He might have reigned much longer had he not erred and turned aside from the right way, and so brought judgment upon himself.