Musar zu Bereschit 18:11

The expression used by the Torah for Joseph, i.e. בן זקונים, also contains an allusion to Adam and Eve, who were the "oldest" people in the world -the first human beings. The Torah wanted to hint that Joseph was a branch of that first pair of human beings in terms of their purity. Just as Adam and Eve had not been the products of the טפה סרוחה, the "evil smelling drop of semen" described by Akavyah in Avot 3,1, so similarly Joseph's origin was pure. The next pair of human beings to whom the Torah applies the term “זקנים,” were Abraham and Sarah in Genesis 18,11, for they took the place of Adam and Eve. We have discussed all this at length in our commentary on חיי שרה. The process of refinement, the road to regaining the innocence and purity lost by Adam, continued through Jacob called Israel because he had successfully contended with heavenly forces. In our classic literature this Israel is referred to as ישראל סבא, grandfather Jacob, whereas Joseph is simply referred to as the son, בן.