וַיִּקְח֞וּ כָּל־עַ֤ם יְהוּדָה֙ אֶת־עֲזַרְיָ֔ה וְה֕וּא בֶּן־שֵׁ֥שׁ עֶשְׂרֵ֖ה שָׁנָ֑ה וַיַּמְלִ֣כוּ אֹת֔וֹ תַּ֖חַת אָבִ֥יו אֲמַצְיָֽהוּ׃
And all the people of Judah took Azariah, who was sixteen years old, and made him king in the room of his father Amaziah.
Read midrashic interpretation of II Kings 14:21: and classical rabbinic exegesis.