Abraham’s rekindled potency causing the birth of Isaac wasn’t a one-time flash in the pan. Abe lived 26 years after that, Sarah died, and Abe remarried and sired 6 more children. Look it up.
Abraham's potency is not the chief miracle here, but rather Sarah's fertility. Not only is she barren, but also she is post-menopausal (Gen. 18:11: "Sarah was past the age of childbearing"); as she describes herself, "Sarah laughed to herself as she thought, “After I am worn out..."" Or as Abraham notes in Gem. 17:17, "Abraham fell facedown; he laughed and said to himself, “Will a son be born to a man a hundred years old? Will Sarah bear a child at
the age of ninety?”
"Abraham lived a hundred and seventy-five years." Gen. 25:7 So I see him living until Isaac was seventy-five years of age.