The tree of life was not forbidden before the fall so it might take centuries
What if Adam found the tree of life and ate of it and afterward ate of the tree of knowledge of good and evil? Do not underestimate the extraordinary thing that God is doing. By definition, you cannot have eternal life if it is possible for you to die. God knows how to eliminate that possibility. It appears that it involves death and resurrection
From what I understand about God’s character, I don’t think God would have put Christ on the cross if there were an easier way to accomplish what he is doing. The trinity of birth, death and resurrection is established. God declaring the end from the beginning has illustrated it the first three versus of Genesis.
Heb 12:2 Looking unto Jesus the author and finisher of our faith; who for the joy that was set before him endured the cross, despising the shame, and is set down at the right hand of the throne of God.