בֶּן־שְׁמוֹנֶ֥ה שָׁנִ֖ים יֹאשִׁיָּ֣הוּ בְמָלְכ֑וֹ וּשְׁלֹשִׁ֤ים וְאַחַת֙ שָׁנָ֔ה מָלַ֖ךְ בִּירוּשָׁלִָֽם׃
Josiah was eight years old when he began to reign; and he reigned thirty and one years in Jerusalem.
Read midrashic interpretation of II Chronicles 34:1: and classical rabbinic exegesis.