How old was Isaac when Jacob and Esau were born?

Answer: 60 years old

Isaac was forty when he married Rebekah and sixty years old when she gave birth to the twins Esau and Jacob.

“and Isaac was forty years old when he married Rebekah, the daughter of Bethuel the Aramean from Paddan-aram and the sister of Laban the Aramean. After this, his brother came out grasping Esau’s heel; so he was named Jacob. And Isaac was sixty years old when the twins were born.”— Genesis 25:20, 25:26 (BSB)