The universe is 6000 years old.
You are not alone in that assessment, but I am afraid I think that is not very likely to be true. The universe at least appears to be far older. I can suppose it true that God simply created it 6000 years ago so that it would simply look older than it is. But why would He? Its not like He has to wait around and be patient. He can create it with a back story like an author writing a book.
Consider JRR Tolkien creating the history of Middle Earth. He is not in the timeline of Middle Earth, he transcends it. The history of Middle Earth is far longer than however long JRR Tolikein spent dreaming it up.
Look at it from God's point of view in the narrative in Genesis that had the six days of creation. God was taking actions in those days. But God does not operate within our timeline. He transcends time and space and is eternal.
Now a human author writing a fantasy book can only put in a make-believe back story to their fictional world. I expect God would put in a real one. But I can't prove that contention. God is a heck of a lot smarter than me, and does as He wills.