Genesis 21:2

21:2 So Sarah became pregnant ¹  and bore Abraham a son in his old age at the appointed time that God had told him.

Genesis 21:5

21:5 (Now Abraham was a hundred years old when his son Isaac was born to him.) ² 

¹ tn Or “she conceived.”

² tn The parenthetical disjunctive clause underscores how miraculous this birth was. Abraham was 100 years old. The fact that the genealogies give the ages of the fathers when their first son is born shows that this was considered a major milestone in one’s life (G. J. Wenham, Genesis [WBC], 2:80).