Rashi, on Gen 25:26

“Isaac was threescore years old when the children were born unto him.”

“בעקב עשו ESAU’S HEEL — a sign that this one (Esau) will hardly have time to complete his period of domination before the other would rise and take it (his power) from him ויקרא שמו יעקב AND HE CALLED HIS NAME JACOB — The Holy One, blessed be He, thus named him (Midrash Tanchuma, Shemot 4). [Some versions add: He said to them (to those who gave Esau that name cf. Genesis 5:25): You have given your first-born a name, I, too, will give my son, my firstborn, (cf. Exodus 4:23) a name. That is what is written, “And He called his name, Jacob” (Genesis 26:26).] Another explanation is: his father called him Jacob because he was grasping Esau’s heel. בן ששים שנה THREESCORE YEARS OLD — Ten years passed from the time when he married her until she became thirteen years old and capable of child-bearing, and a further ten years he hopefully waited as his father did in regard to Sarah. When even then she did not become with child he realised that she was barren and he prayed for her. But He did not wish to take a maidservant as a second wife because he had been sanctified on Mount Moriah to be a burnt-offering without blemish.”

Imported from an open dataset — not yet checked against the printed edition.