Classical Torah vs. Chabad: Age of the Universe
The prior Chabad Rebbe zt"l (who passed away in 1994) in an article "Theories of Evolution" on the chabad dot org website offers several explanations for a young Earth creation theory. The prior Rebbe suggests that God could have created fossils of dinosaur bones, despite the fact that living dinosaurs never actually existed.
The prior Chabad Rebbe also cites some earlier sources about an ancient Universe, and then claims that a ruling ("psak") was reached by the Arizal in this matter.
The claim that there is some kind of "psak" on the age of the Universe has no basis, not according to myself but according to Rambam. Nowhere does Rambam seem to state the age of the Universe, on the contrary in Moreh Nevuchim 2:13 the Rambam seems to equate such statements with heretical Aristotelian beliefs in an eternal Universe.
I believe Rabbi Aryeh Kaplan zt"l stated there is no Torah source that Hashem created bones of animals that never actually existed.
The notion that God would create fossil bones of animals that never existed would seem to conflict with the statement in the Talmud that "God's seal is truth".
The Rebbe writes that "This interpretation is indeed offered in several books", IE the belief in an ancient Universe. The "books" the Rebbe is referring to include Breisheet Rabbah, IE the Midrash written by the ancient rabbis. The opinion of these ancient rabbis cannot simply be swept under the rug because they conflict with Chabad doctrine.
The treatise "Drush Ohr HaChaim" written by the great 19th Century Torah sage Tiferet Israel (and printed in some editions of the Talmud Sanhedrin) cites the ancient Torah sources (the "books" rejected by the Rebbe) to prove that an ancient Universe is not in conflict with the Torah.
I don't believe Chabad can simply override the opinions of the ancient rabbis with an alleged "psak". There is no "psak" on such matters without a prophet or at least a Sanhedrin. Arizal was not a posek. The writings attributed to him were actually written by later people after he passed away, these writings have become more like mythology inserted into Judaism.