I’m confused exactly what’s causing you difficulty in understanding this. Can you spell it out more carefully (ideally in some formal language)? As far as I can gather you are saying something along the lines of:
These premises are not consistent:
(1) God is eternal.
(2) God created the universe.
(3) The universe was created at a finite point in time.
The point is a little hard to grasp but lets see if I can make it easier: Our universe has a specific age. One can ask a question whether God can create an older or a younger universe? For older universe God should wait a little longer before the act of creation, but God cannot wait longer since he is timeless. In another point there is no time reference point in God’s mind for any action hence timeless God cannot create anything. And this is the paradox for timeless God.
But these seem to be consistent so I’ll wait for clarification before responding.
I hope that clear now. To be honest paradox even apply for the case that universe is not caused by God and it is the result of an accident.