Our Gemara on Amud Aleph delves into the stages of maturity and de-facto challenges the popular misconception that reaching the age of bar or bas mitzvah automatically grants full adulthood according to Jewish law. The rabbis recognized that maturity and judgment are not black-and-white distinctions, as evidenced by their ruling that individuals under the age of 20 do not possess the full capacity to sell inherited real estate. In addition, Gemara Shabbos (89b) holds that one is not liable for heavenly punishments until age 20.
Modern brain research, facilitated by functional MRIs, allows us to measure and understand the developmental processes of the brain. It is widely known that the brain undergoes continued growth and change throughout adolescence, particularly in areas associated with judgment and executive functions. Researchers Johnson and Blum highlight this in their study on adolescent maturity and brain development, emphasizing that the frontal lobes, responsible for crucial executive functions such as planning, impulse control, and working memory, may not fully mature until the mid-20s (Johnson & Blum, J Adolesc Health. 2009).
The rabbis, through their observations and common sense, if not tradition, were also quite aware of the incomplete development of certain executive functions during adolescence.
An intriguing question arises regarding the biblical story of Yaakov purchasing the birthright from Esau. According to tradition, both twins were of bar mitzvah age, but not older (Rashi on Genesis 25:27). Yismach Moshe raises a significant concern regarding the sale of the birthright, as Esau's consent may have been invalid due to his immaturity at that age.
To address this concern, Yismach Moshe provides a new reading and pilpul into the following verses (Genesis 25:31-32):
וַיֹּ֖אמֶר יַעֲקֹ֑ב מִכְרָ֥ה כַיּ֛וֹם אֶת־בְּכֹרָֽתְךָ֖ לִֽי׃
Jacob said, "Sell me your birthright as of today."
וַיֹּ֣אמֶר עֵשָׂ֔ו הִנֵּ֛ה אָנֹכִ֥י הוֹלֵ֖ךְ לָמ֑וּת וְלָמָּה־זֶּ֥ה לִ֖י בְּכֹרָֽה׃
And Esau said, "Look, I am about to die, so what good is this birthright to me?"
The Gemara Bava Basra (16b) tells us that it was busy day for Esau, to say the least:
אָמַר רַבִּי יוֹחָנָן חָמֵשׁ עֲבֵירוֹת עָבַר אוֹתוֹ רָשָׁע בְּאוֹתוֹ הַיּוֹם בָּא עַל נַעֲרָה מְאוֹרָסָה וְהָרַג אֶת הַנֶּפֶשׁ וְכָפַר בָּעִיקָּר וְכָפַר בִּתְחִיַּית הַמֵּתִים וְשָׁט אֶת הַבְּכוֹרָה
Rabbi Yoḥanan says: That wicked Esau committed five transgressions on that day that Abraham died: He engaged in sexual intercourse with a betrothed maiden, he killed a person, he denied the principle of God’s existence, he denied resurrection of the dead, and he despised the birthright.
בָּא עַל נַעֲרָה מְאוֹרָסָה כְּתִיב הָכָא וַיָּבֹא עֵשָׂו מִן הַשָּׂדֶה וּכְתִיב הָתָם כִּי בַשָּׂדֶה מְצָאָהּ הָרַג אֶת הַנֶּפֶשׁ כְּתִיב הָכָא עָיֵף וּכְתִיב הָתָם אוֹי נָא לִי כִּי עָיְפָה נַפְשִׁי לְהֹרְגִים וְכָפַר בָּעִיקָּר כְּתִיב הָכָא לָמָּה זֶה לִי וּכְתִיב הָתָם זֶה אֵלִי וְאַנְוֵהוּ וְכָפַר בִּתְחִיַּית הַמֵּתִים דִּכְתִיב הִנֵּה אָנֹכִי הוֹלֵךְ לָמוּת וְשָׁט אֶת הַבְּכוֹרָה דִּכְתִיב וַיִּבֶז עֵשָׂו אֶת הַבְּכוֹרָה
The Gemara cites proofs to support these charges. He engaged in sexual intercourse with a betrothed maiden, as it is written here: “And Esau came in from the field”; and it is written there with regard to rape of a betrothed maiden: “For he found her in a field” (Deuteronomy 22:27). He killed a person, as it is written here: “And he was faint”; and it is written there: “Woe is me, for my soul faints before the slayers” (Jeremiah 4:31). And he denied the principle of God’s existence, as it is written here: “What profit is this to me” (Genesis 25:32); and it is written there: “This is my God and I will glorify Him” (Exodus 15:2). When he questioned the profit of “this,” he was challenging the assertion that “this is my God.” And he denied resurrection of the dead, as it is written: “Behold, I am at the point of death” (Genesis 25:32), indicating that he did not believe in resurrection after death. And he despised the birthright, as it is written: “And Esau despised the birthright” (Genesis 25:34).
Yismach Moshe suggests that the last three sins attributed to Esau—denying the principle of God's existence, denying resurrection of the dead, and despising the birthright—were committed stubbornly after he had already agreed to sell it. However, the first two sins, engaging in sexual relations with a betrothed maiden and committing murder, may have occurred prior to the sale. Yismach Moshe argues that The sin of murder is only derived from a comparison to a verse in Yirmiyahu and thus can be seen as an indirect suggestion but not actual murder, i.e. Esau had murderous intentions. However the adultery is derived from a verse in the Pentateuch and therefore is literal. But, whether Esau's act of having relations with a betrothed maiden constituted adultery depends on whether he is viewed as a Jew or a gentile. Marriage to a gentile is established by cohabitation, thus the engaged and betrothed maiden is not considered married according to gentile law.
Additionally, there is a rule that different thresholds of liability apply to Jews and gentiles. While Jews have specific ages of obligation, gentiles are judged based on their ability to understand the consequences of their actions. (See Rambam Laws of Kings 9:9-10 and Mincha Chinuch 190:8.) Therefore, Yaakov makes the following lomdishe argument: "While you might claim that you were not competent enough to agree to sell your birthright, that argument is valid only if you were considered to be Jewish. However, if you are not Jewish, we do not apply those rules, and you have enough reason and ability to agree to the sale. If you claim to be Jewish, you would be liable for death for having committed adultery." This is why Esau declares, “I am at the point of death, of what use is the birth rate to me?” That is to say, if I try to hold onto the birthright through this legal argument, then I also will be considered Jewish and liable for the death penalty.
This analysis by Yismach Moshe is a clever derush that showcases his Talmudic expertise and creativity. However, it may not reflect the straightforward peshat (simple interpretation) of the text.
The idea that gentiles would not be subject to legal threshold, and the law would be applied in a more common sense fashion, as opposed to Jews, requires some analysis. Why should this be true? I don’t have a complete answer, but I think it has to do with something along these lines. Jews are engaged in a covenantal relationship with God. When there is a covenant, there is an agreement, and there are rules. On the other hand, other human beings who are also children of God, do not have a covenant. That can go both ways. There are less formal obligations, but also because there is no legal framework, obligations are based on the varying conditions of the moment. So, in some ways , they could end up becoming more liable not less. A famous halakhic example of this is that the both Jew and gentile are forbidden to eat flesh taken from an animal while it is still alive. But the definition of “live” changes from gentle to Jew. Since a gentile does not have the obligation of ritual slaughter, the animal is dead only when it stops moving and is completely devoid of life. However, for the Jew, the animal is dead the moment the shechitta is performed properly. Therefore, while the animal is still thrashing about after the slaughter, a Jew may eat from that meat, while a gentile is forbidden (see Chulin 33a.) We see the covenantal nature of Torah law can sometimes Eva me more leniency than the Seven Noachide Laws.
Translations Courtesy of Sefaria, except when, sometimes, I disagree with the translation 
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