His voice changed
In question: His voice deepened from that of a child to that of a young man.
(Modern Hebrew)
Translation
Expression (Hebrew)
הִתְחַלֵּף לוֹ הַקּוֹל
Definition (Hebrew)
בְּהַשְׁאָלָה: קוֹלוֹ הִתְעַבָּה מִקּוֹל שֶׁל יֶלֶד לְקוֹל שֶׁל נַעַר.
(הָעִבְרִית הַחֲדָשָׁה)