He is still a boy (childish)
The person being spoken to is still young for days, and his age should not be ignored (and the youth is still young).
("And he went up with her, as she had done, with three bullocks, and an ephah of flour, and a bottle of wine, and brought them to the house of the Lord, to Shiloh. And the boy was young" - Samuel 1:1 (about Hannah bringing her son Samuel to her sanctuary), and also: "While the boy was still young, he began to draw a scribe's staff, and whatever he saw in his heart he wrote in a book" - Agnon/ City and its Fullness, 554)
Translation
Expression (Hebrew)
וְהַנַּעַר נָעַר
Definition (Hebrew)
הַמְּדֻובָּר עֲדַיִין בְּאָדָם צָעִיר לְיָמִים וְאֵין לְהִתְעַלֵּם מִגִּילוֹ (וְהַנַּעַר עֲדַיִין צָעִיר).
("וַתַּעֲלֵהוּ עִמָּהּ כַּאֲשֶׁר גְּמָלַתּוּ בְּפָרִים שְׁלֹשָׁה וְאֵיפָה אַחַת קֶמַח וְנֵבֶל יַיִן וַתְּבִאֵהוּ בֵית ה' שִׁלוֹ. וְהַנַּעַר נָעַר"- שְׁמוּאֵל א א כַּד (עַל חַנָּה הַמְּבִיאָה אֶת בְּנָהּ שְׁמוּאֵל לַמִּקְדָּשׁ שֶׁלָּהּ), וְכֵן:"עוֹד הַנַּעַר נַעַר הֵחֵל לִמְשֹׁךְ בְּשֵׁבֶט סוֹפֵר, וְאֶת אֲשֶׁר רָאָה לִבּוֹ כָּתַב בַּסֵּפֶר"-עַגְנוֹן/ עִיר וּמְלוֹאָהּ, 554)