I'm dubious about the recent claim that Isaac was a full grown adult at the time Abraham was commanded to sacrifice him. Over and over the scriptures call it a trial for Abraham. Abraham gets great blessings for it.
No one involved or in the following years in the scripture describe it as a test of Isaac's faith. That seems to all be a recent "discovery". More interestingly, Abraham received great blessings for it, as the scriptures and Joseph Smith describe. If Isaac had really been being tested to see if he would obey as well, then Isaac should have received comparable blessings.
I just don't believe in the modern "discovery" that Isaac was an adult at the time Abraham was commanded to sacrifice him. There is so much scripture that it runs counter to - because if he was an adult everyone would have recognized that he was being tried, and there is no mention anywhere the Isaac proved faithful and received comparable divine blessings to Abraham for that experience. I think all those easily outweigh the scriptures used to calculate Isaac's age.