There are only 2 rational explanations for how God created the Universe.
Option #1.
Around 14 billion years ago God created the Universe - He did it using physical processes and set all of the physical laws and rules in place for it to work just fine without him...
Option 2.
Around 6 thousand years ago God created the entire universe in 6 days - however he created it to look much older...
I believe there is a third option.
Option #3
God did just what you said in option #1.
The Bible is about Adam's creation in the image of God...after this period.
The world in Genesis started with the world covered with water, from a previous destruction.
The six thousand year period is only from that time forward to Adam, because the Bible is about Adam - a son of God.
This is about the creation of God in this realm.
Adam was not just a man. He was a son of God, a order of life higher than the angels.
But he fell and lost the rights to this world.
Jesus bought back the rights to it.
Satan attempting to bring this plan to an end, just played into God's hands by providing the adversity to mold the character of God into His children.
This third option explains why a six thousand year period is mentioned but the earth is much older.
Don't take what theologians tell you the Bible says...
They have all interpreted it wrong.
Some hit and miss, but for the most part wrong.
Don't take what the scientist's tell you they see in nature as the whole story either...
They have left out much about our history.
They hit and miss, and discover much that is true.
But they have only scratched the surface of what's there is to know.
The truth is seldom found to be in one extreme or the other...
It is usually somewhere in between resting in a perfect balance of both sides.
That is where you'll find Option #3.