Age of Isaac When Abraham Offered Him as a Sacrifice?

I would like to know, if possible, at least the approximate age of Isaac when Abraham offered him as a sacrifice to God. Based on Abraham's advanced age, it would seem that Isaac did not resist in being bound to the wood. Also, it seems that he was no toddler since he helped carry the wood that he was to be bound to. Has a reasonable estimate of Isaac's age ever been ascertained at the time of his sacrificial offering to God? Thank you.