Comentário sobre Gênesis 16:16

'ואברם בן שמנים שנה וגו AND ABRAM WAS FOURSCORE AND SIX YEARS OLD etc. — This is written to Ishmael’s credit, pointing out that he was thirteen years old when he was circumcised (see Genesis 17:25) and yet he raised no objection.

ואברם בן שמנים שנה ושש שנים, the reason why the Torah tells us Avram's age at the time Ishmael was born is to inform us that he was born in the same year Sarai had given Hagar to Avram in order to provide him with offspring. Avram was to rejoice over the prompt success of the arrangement. We know that Avram was 75 years old when he moved to the land of Canaan so that he must have been 85 years old at the end of the 10 years mentioned previously. (16,3). The word מקץ in that verse refers to the end of a period, i.e. the end of 10 years residence in the land of Canaan. We encounter the word מקץ as also meaning "at the end of" in Deut. 15,1 מקץ שבע שנים תעשה שמטה, "at the end of seven years (a cycle) you are to make a release," (forgive past due loans.)

To let us know that he was thirteen years old ... For Avraham was 99 when he circumcised Yishmael, and he was 86 when Yishmael was born. You might ask: [If the reason is as Rashi says,] why is it expressly written, “And his son Yishmael was 13 years old when he circumcised...” (17:25)? The answer is: Scripture repeats it to emphasize that Yishmael circumcised himself because of Hashem’s mitzvah, not from fear of his father who obliged him to do it. But the Mahara’i answers: We would not know from v. 17:25 that Yishmael was a full 13 years old, which is the age of attaining maturity, [for it could mean he was just over 12, and thus still a minor,] and that is why he did not resist. But the verse here makes the point clear.