And Abraham was ninety years old and nine, when he was circumcised in the flesh of his foreskin.
Read Chapter 17
John Chrysostom
AD 407
Don’t think it was without purpose that Scripture indicated to us his age; instead, it was for you to learn from the just man’s obedience in meekly submitting to pain despite his extreme old age on account of God’s command, and not only he but also Ishmael and all the servants—that was the reason for giving the ages.