Genesis 17:12

Days, when he will be able to bear the pain without danger. This might be deferred for a just reason, as it was in the desert, Josue v. 6. In this case people might be saved, as younger children and all females might, by the application of the remedies used in the law of nature, sacrifice, the faith of parents, &c. (Menochius) --- Of your stock, and, being arrived at years of discretion, is desirous of enjoying your privileges. Some think, that slaves had no choice left; but servants, and people who had a mind to live in the country, were not bound to submit to this rite against their will. It is even more probable, that none were under this obligation, except Abraham and his posterity by Isaac. His other children adopted it in part, but not with the exactitude of the Jews. (Calmet)