Zohar Chadosh, Bereishis 15:4.
With Bar Mitzvah, the person is entering stage of being exposed to Yezter Hara, i.e. his priveliledges come with responsibilities to overcome inner struggles and temptations. Commenting on Ecclesiastes, Rashi lays down the overall process that someone to come to the age of Bar Mitzvah experience:
טוֹב יֶלֶד מִסְכֵּן וְחָכָם מִמֶּלֶךְ זָקֵן וּכְסִיל. טוֹב יֶלֶד מִסְכֵּן וְחָכָם, זֶה יֵצֶר טוֹב, וְלָמָּה נִקְרָא שְׁמוֹ יֶלֶד, כִּי אֵין מִזְדַּוֵּג לָאָדָם אֶלָּא מִבֶּן שְׁלשׁ עֶשְׂרֵה שָׁנָה וּלְמַעְלָה, וְלָמָּה נִקְרָא שְׁמוֹ מִסְכֵּן, שֶׁאֵין הַכֹּל שׁוֹמְעִין לוֹ. וְלָמָּה נִקְרָא שְׁמוֹ חָכָם, שֶׁהוּא מְלַמֵּד אֶת הַבְּרִיּוֹת לְדֶרֶךְ יְשָׁרָה. מִמֶּלֶךְ זָקֵן וּכְסִיל, זֶה יֵצֶר הָרָע, וְלָמָּה קוֹרֵא אוֹתוֹ מֶלֶךְ, שֶׁהַכֹּל שׁוֹמְעִין לוֹ, וְלָמָּה קוֹרֵא אוֹתוֹ זָקֵן, שֶׁהוּא מִזְדַּוֵּג לוֹ מִיַּלְדוּתוֹ וְעַד זִקְנָתוֹ. וְלָמָּה קוֹרֵא אוֹתוֹ כְּסִיל, שֶׁהוּא מְלַמֵּד לְאָדָם לְדֶרֶךְ רָעָה. אֲשֶׁר לֹא יָדַע לְהִזָּהֵר עוֹד, שֶׁאֵינוֹ יוֹדֵעַ כַּמָּה צַעַר וְכַמָּה יִסּוּרִין בָּאִין עָלָיו וְהוּא אֵינוֹ נִזְהָר מֵהֶם.
“Better is a poor and wise child than an old and foolish king who no longer knows to receive admonition” (Ecclesiastes 4:13).
“Better is a poor and wise child than an old and foolish king.” “Better is a poor and wise child” – this is the good inclination. Why is it called a child? Because it only associates with a person from the age of thirteen onward. Why is it called poor? It is because not everyone heeds it. Why is it called wise? It is because it guides people to the straight path. “Than an old and foolish king” – this is the evil inclination. Why is it called “king”? It is because everyone heeds it. Why is it called “old”? It is because it associates with him from his youth through his old age. Why is it called a “fool”? It is because it guides a person to an evil path. “Who no longer knows to receive admonition” – he does not know how much pain and how much suffering will afflict him, but he is not cautious in their regard.


