2 Chronicles 24:1

Overview - 2 Chronicles 24
Joash reigns well all the days of Jehoiada.
He gives order for the repair of the temple.
15 Jehoiada's death and honourable burial.
17 Joash, falling into idolatry, slays Zechariah the son of Jehoiada.
23 Joash is spoiled by the Syrians, and slain by Zabad and Jehozabad.
27 Amaziah succeeds him.
Treasury of Scripture Knowledge

2 Chronicles 24:1  (King James Version)
Joash was seven years old when he began to reign, and he reigned forty years in Jerusalem. His mother's name also was Zibiah of Beersheba.

M. 3126-3165. B.C. 878-839. Joash.
Joash, [Ywsh ,] is merely an abbreviation
of Jehoash, [Yehw'sh ,] by the elision of [H,] {hay,} and here also of [Vv,] {wav.} 2 Kings 11:21 ; 12:1

1 Chronicles 3:11

seven years old
As Joash was hidden six years in the temple, and was but seven when he came to the throne, he could have been but one year old when secreted by his aunt.