2 Chronicles 34:1

Josiah [was] eight years old when he became king, and he reigned thirty-one years in Jerusalem.

Jeremiah 1:2

[to] whom the word of Yahweh came in the days of Josiah the son of Amon, the king of Judah, in the thirteenth year of his reign.

Zephaniah 1:1

The word of Yahweh that came to Zephaniah the son of Cushi, the son of Gedaliah, the son of Amariah, the son of Hezekiah, in the days of Josiah son of Amon, king of Judah.

1 Samuel 2:18

Now Samuel [was] serving before Yahweh, as a boy wearing a linen ephod.

1 Samuel 2:26

But the boy Samuel {continued to grow in stature and in favor} with Yahweh and with the people.

1 Kings 3:7-9

So then, O Yahweh, you are my God. You have made your servant king in place of David my father [though] I [am] a young boy. I do not know going out or coming in.

1 Kings 13:2

Then he proclaimed against the altar by the word of Yahweh and said, "O altar, altar, thus says Yahweh: 'Look, a son will be born to the house of David, Josiah by name, and he shall sacrifice on you the priests of the high places who burn incense on you, and human bones shall burn on you.'"

2 Kings 22:1-20

Josiah was eight years old when he began to reign, and he reigned thirty-one years in Jerusalem. The name of his mother [was] Jedidah the daughter of Adaiah from Bozkath.

1 Chronicles 3:14-15

Amon [was] his son, Josiah [was] his son.

2 Chronicles 24:1

Joash [was] seven years old when he became king, and he reigned forty years in Jerusalem. And the name of his mother [was] Zibiah from Beersheba.

2 Chronicles 26:1

Then all the people of Judah took Uzziah (now he [was] sixteen years old) and made him king in the place of his father Amaziah.

2 Chronicles 33:1

Manasseh [was] twelve years old when he began to reign, and he reigned fifty-five years in Jerusalem.

2 Chronicles 33:25

But the people of the land struck down all who conspired against King Amon. And the people of the land made his son Josiah king in his place.

Ecclesiastes 4:13

A poor but wise youth [is] better than an old but foolish king who no longer knows {how to receive advice}.

Matthew 1:10-11

and Hezekiah became the father of Manasseh, and Manasseh became the father of Amon, and Amon became the father of Josiah,

Treasury of Scripture Knowledge

Summary

Josiah was eight years old when he began to reign, and he reigned in Jerusalem one and thirty years.

Bible References

Eight years

2 Chronicles 24:1
Joash [was] seven years old when he became king, and he reigned forty years in Jerusalem. And the name of his mother [was] Zibiah from Beersheba.
2 Chronicles 26:1
Then all the people of Judah took Uzziah (now he [was] sixteen years old) and made him king in the place of his father Amaziah.
2 Chronicles 33:1
Manasseh [was] twelve years old when he began to reign, and he reigned fifty-five years in Jerusalem.
1 Samuel 2:18
Now Samuel [was] serving before Yahweh, as a boy wearing a linen ephod.
1 Kings 3:7
So then, O Yahweh, you are my God. You have made your servant king in place of David my father [though] I [am] a young boy. I do not know going out or coming in.
Ecclesiastes 4:13
A poor but wise youth [is] better than an old but foolish king who no longer knows {how to receive advice}.