Which king began to seek the God of his father David in the eighth year of his reign, while still young?

Answer: Josiah

In his eighth year, while still young, Josiah began to seek God; in his twelfth year he began purging Judah and Jerusalem of idols.

“In the eighth year of his reign, while he was still young, Josiah began to seek the God of his father David, and in the twelfth year he began to cleanse Judah and Jerusalem of the high places, the Asherah poles, the carved idols, and the cast images.”— 2 Chronicles 34:3 (BSB)