One argument I have heard in favor of an old Earth, and Universe, has to do with the stars.
When you look at a star today you are seeing it how it was years ago, depending on its distance. Some of the closest stars are about 100 light years away but some of the more distant ones might be as many as a million light years away.
So you are seeing that star how it looked a million years ago. If it even existed then. Certainly it is possible for God to create the star more recently but with a light trail that APPEARS to be a million light years long, but that seems to go against God’s nature since it would be very strange for God to create something with deception in mind.
So that would seem to point to an old earth/old universe. With Genesis 1 explaining more of a hierarchy of creation rather than an actual time frame. (Remember a day to the Lord is like 1,000 years).
There is another possibility too. Like Einstein said “time is relative”. Since time and space are woven together in a “fabric” called “space/time”, perception of time will be different depending on your position in space. 1 day in God’s eyes could literally be a million years in mans eyes.
It gets complex, but that is something to think about.
I think there was a book called “Genesis and the Big Bang” where I read some of that.