
IMO the main problem is unfalsifiability. “Creatio ex nihilo” necessarily implies the illusion of greater age than a system’s “true age”*. So no matter how much evidence there is that the world is older than 7k years, it’s never truly evidence in their minds. *At least, with respect to a closed thermodynamic system that is characterized by chronological, cause-effect relations like our world is.
Sorry! Essentially YECs believe that the entire universe was spawned out of nothing, more or less instantaneously. When you combine that with the universe being 1) run on principles of cause and effect, and 2) a closed thermodynamic system (no energy created or destroyed), you get what’s called “the illusion of age”. So YEC presupposes that no matter what, the world will SEEM older than it really is. Therefore, no amount of proof of an old earth can ever invalidate their position.