וְיוֹסֵף֙ בֶּן־שְׁלֹשִׁ֣ים שָׁנָ֔ה בְּעָמְד֣וֹ לִפְנֵ֔י פַּרְעֹ֖ה מֶ֣לֶךְ מִצְרָ֑יִם וַיֵּצֵ֤א יוֹסֵף֙ מִלִּפְנֵ֣י פַרְעֹ֔ה וַֽיַּעֲבֹ֖ר בְּכׇל־אֶ֥רֶץ מִצְרָֽיִם׃
And Yosef was thirty years old when he stood before Pharaoh king of Egypt. And Yosef went out from the presence of Pharaoh, and went throughout all the land of Egypt.
Bereishis Rabbah 90:4 concludes with Yosef’s age of thirty; the separate maxim “בן שלשים לכח” is from Mishnah Avot 5:21.
Sefaria · Bereishis Rabbah 90:4 · Sefaria · Pirkei Avot 5:21
וְיוֹסֵף בֶּן שְׁלֹשִׁים שָׁנָה. בֵּן שְׁלֹשִׁים לַכֹּחַ (אבות ה, כא) – וְכָאן עָמַד לְפָנֵי מֶלֶךְ.
English: “And Yosef was thirty years old.” The page’s “thirty for strength” maxim comes from Mishnah Avot 5:21, while Bereishis Rabbah 90:4 itself closes by noting Yosef’s age of thirty.
On the daf / in context: The two source strands can be read together as a homiletic application: the Midrash supplies the age, and Avot supplies the maxim about thirty and strength.
Type of Learning: Derash on the verse (classic midrash / chronological) — not a formal named middah of the 13.
What Is Learned: Yosef reaches the age of full strength precisely when he is elevated to rule; the years of hardship prepared him for the moment of public responsibility.