Commentaire sur La Genèse 26:34

בן ארבעים שנה [AND ESAU WAS] FORTY YEARS OLD —Esau is compared to a boar, as it is said, (Psalms 80:14) “The boar from the wood doth ravage it”. The boar when it lies down stretches forth its cloven hoof as much as to say, “See, I am a clean animal” (whilst really cloven hoofs are a feature of clean animals only in conjunction with another that is lacking in the swine). In the same way these dukes of Esau rob and extort and pretend to be honorable (Genesis Rabbah 65:1). For the whole forty years Esau enticed women from their husbands and ill-treated them; when he reached the age of forty he said, “My father took a wife when he was forty and I shall do the same” (Gen. R. 65).

ויהי עשו בן ארבעים שנה, at that point Yitzchok was 100 years old seeing that he had been 60 years old at the time the twins had been born. The only reason the Torah draws our attention to the age at which Esau got married was to give us a better understanding of Yitzchok’s age when he is described as getting old, (27,1) He must have been well over 100 years old by then.

ויהי עשו בן ארבעים שנה, at that point Yitzchok was 100 years old and he did not bother to see to it that both of his sons should be provided with suitable wives. As a result,