Question: How old were Isaac and Rebekah when Jacob and Esau were born – 63 and 23 years?
Answer: The verse (Gen. 25:26) explicitly records Isaac’s age at the birth of his two sons to be 60 years old. In Gen.25:20 we learn that he married Rebecca at age 40. Therefore, if, as much of the rabbinic chronology indicates, she was 3 at the time of marriage she would have given birth, as you suggested, at age 23. However, there are opinions that she was older (for example Ibn Ezra) at the time of her marriage to Isaac.
All the best,
R’ Daniel Fleksher