For in the eighth year of his reign, while he was yet a boy, he began to seek the God of David his father, and in the twelfth year he began to purge Judah and Jerusalem of the high places, the Asherim, and the carved and the metal images.
Concerning Josiah we are here told, 1. That he came to the crown when he was very young, only eight years old (yet his infancy did not debar him from his right), and he reigned thirty-one years (Ch2 34:1), a considerable time.
Commenting on 2 Chronicles 34:1-7
And they broke down the altars of Baalim in his presence,.... He not only ordered them to be broke down, but he went in person, and saw it done; these were the altars Manasseh had reared up to the idols; and though upon his humiliation he cast them out, they were rebuilt by Amon his son, see Ch2 33:3, and the images that were above...
HE DESTROYS IDOLATRY. (Ch2 34:3-7) in the eighth year of his reign--This was the sixteenth year of his age, and, as the kings of Judah were considered minors till they had completed their thirteenth year, it was three years after he had attained majority. He had very early manifested the piety and excellent dispositions of his character.