2 Chronicles 34:3

For in the eighth year of his reign, while he was yet (b) young, he began to seek after the God of David his father: and in the twelfth year he began to purge Judah and Jerusalem from the high places, and the groves, and the carved images, and the molten images.

(b) When he was but sixteen years old he showed himself zealous of God's glory, and at twenty years old he abolished idolatry and restored the true religion.