“Apparent age” means that God created the cosmos to look billions of years old when in fact it is only a few 1000 years old.
That's a misleading way of putting it. Mature creation isn't like antiquing an object to make it look older than it really is by artificial means. Rather, the theory of mature creation is that to create anything ex nihilo is to go from absolutely nothing to something concrete, thereby skipping over what would normally be the intervening stages in a cyclical process to arrive at that instantaneous result. Once a cycle is in place, there's a continuum to how things come into being, persist, and cease to exist. But creating the initial conditions is discontinuous with the status quo.
You may still reject mature creation, but you need to be clear on what the position represents.