Both can be true. God created the universe 4000 years ago, but did so by creating in his mind a big bang and fast-forwarding time to 2000BC. Then instantiating physically what he was thinking of.
Given that take - there is no distinction between the universe being billions of years old and the universe having been "fast forwarded" to 2000BC. This is being perceived by an entity that sits outside the passage of time. Everything is arguably "fast forwarded" in that the entirety of creation - along with everything before and after creation - is being experienced simultaneously by a timeless being.
From God's perspective, though, it doesn't matter if the prayer occurs before or after the event, (assuming God exists outside of time and knows everything that has happened and will ever happen).
That might seem to open the possibility that believers could pray for events to be retroactively changed from a known (to them) outcome to a different outcome (rewriting their memories in the process), but presumably the claim is that God's will is revealed through the outcomes themselves, and the believer should update their desires based on that revealed will.