حيث ذهبوا إلى قدم السماوات جواهرها وصورها وأشكالها
For they held the heavens, their substances, forms, and shapes to be eternal.
The claim is not merely that celestial bodies are extremely old. It denies a temporal beginning to them. In the particular Peripatetic account, heavenly bodies were treated differently from mutable terrestrial elements.
This describes a historical philosophical school, not a determination of the age of the universe by contemporary science. The theological question is whether a beginningless portion of the world can be justified by valid reasoning.