26 Then God said, “Let us make mankind in our image, in our likeness, so that they may rule over the fish in the sea and the birds in the sky, over the livestock and all the wild animals,[a] and over all the creatures that move along the ground.”
27 So God created mankind in his own image,
in the image of God he created them;
male and female he created them.
Then the Lord God formed a man[c] from the dust of the ground and breathed into his nostrils the breath of life, and the man became a living being.
8 Now the Lord God had planted a garden in the east, in Eden; and there he put the man he had formed. 9 The Lord God made all kinds of trees grow out of the ground—trees that were pleasing to the eye and good for food. In the middle of the garden were the tree of life and the tree of the knowledge of good and evil.
As I "understood" the story of Genesis Gen 1 is about the world and Gen 2 is about Eden. In Gen 1 it claims that god made "them" mankind plural. So Adam wouldn’t be the first man. Maybe one of the first but he was the dude in Eden who somehow became the representative for all the humans on earth. If you go by this "logic" then the world could be decently populated in 900 years.
I know that this doesn't explain away any of the other contradictions and I don’t mean it to. If you want to do that you are on your own