Commentary for Genesis 43:17

ויעש האיש כאשר אמר יוסף, “the man did as Joseph had said. According to our sages, the “man” was his older son Menashe, [who could not have been more than nine years old at the time. Ed.] This is difficult in light of Rashi’s commentary in the Talmud Avot chapter 5, that the rule that men have to observe the Torah’s commandments from the age of 13, is derived from Shimon and Levi, Joseph’s brothers when we calculate their ages at the time when they took their swords and killed the male population of the town of Sh’chem. (Genesis 34,25) If they were 13 at the time, it is clear that Menashe at this time could not have been older than nine years old. The Torah had spelled out that Joseph’s sons had been born before the onset of the famine. Seven years had elapsed since Joseph had married, seven good years and 2 years of famine. How could the Torah refer to Menashe as a “man” then? (Attributed to Rav Chayim who quoted Rabbi Eliezer avi ha-ezri.) The problem deserves further study.