When I became a Christian I believed in a very old Earth, billions of years etc. But eventually I had to decide whether the Bible was right or wrong. Whether Jesus was wrong when He said Adam and Eve were made in the beginning. Jesus believed in the Old Testament in its entirety and once I had researched this issue, I too came to believe in a young Earth just less than 6000 years old.
So let go, young or old?
Time started with Genesis 1:1
Before time, you should think the Earth was hundreds of millions of years old.
The way it goes to the letter,
is God made dinosaurs, and the world was extremely rainy, because dinosaurs were reptiles, they needed continual rain.
Else their flesh falls off.
then Satan was cast down, and Satan caused the dinosaurs to eat each other.
then God blew on the earth and it froze, and it froze for hundreds of millions of years,
while Satan sat there.. all by himself. It may be better to consider is it hundreds of millions,
or hundreds of billions, just because he was alone, and I don't really know which one it was.
Yes it was very rainy, and in the early days of mankind it was not as rainy, yet they had their drinking water from the dew of the grass, and the flood came, gotta wonder. 2+2=4
God's command also was, "repopulate the Earth"