There are so many problems with this view that I prefer the most ancient of Christianity’s take on this account, namely that neither God nor the Bible writers involved ever expected us to take the account literally.
For example, Gregory Nazianzen (329-390 A.D.) theorized as to the meaning of this story, on this basis of the Church considering it a parable,. Even today Christendom believed the story is explaining not how sin came into the world, but that life in the world is the way it is because of sin. Because of it viewed this way, Nazianzen went into some depth regarding what each element in the narrative meants, something he would not have done if the Christians had believed it was literal—which they did not.
The Tree of Knowledge of Good and Evil, he stated, was “contemplation,” being able to use a well-trained conscience to see if one's own judgment regarding their actions was right morally virtuous and beneficial or not. Was the narrative teaching people that God was forbidding humans from this “Tree”? No, he taught: “God did not forbid it because it was evil from the beginning when planted. Nor did God grudge it to men…But it would have been good if partaken of at the proper time.”
In other words, instead of an “origins of sin” story, Christianity has seen this narrative as exposing a central truth in life: we can’t live our lives without sin's interference because it has been this way with humankind since the beginning. They did not then nor does modern scholarship (especially that governed by the critical sciences) believe it to be a historical account. The point of the narrative is not how sin came into our lives, but how we let it into our lives now which is no different from the way Adam and Eve did then, namely we jump to our own conclusions as to what is right and wrong without training our conscience with God's help. We let how we personally feel on matters be our judge instead of using a God-trained conscience to consider the validity of our judgments.
And while Adam and Eve are considered to be real people, the reason for the type of narrative or genre chosen for this story (namely “fable” or “parable,” i.e., a story with a moral lesson to be learned and carried away) was so that people would not make the same mistake Adam and Eve did. (If we see it as literal, does a moral stand out that is clear to all? As noted by this discussion and others like it, it does not.) Instead we should let God train us until our conscience is ready for “contemplation.” Unless we learn from a more intelligent Source, our decisions can be fatal.
Also, the long years are not literal either. If you notice, this way of counting drops off sharply by the time Abraham* comes on the scene. Critical Biblical analysis teaches that this is a literary device to tell the reader that “fable ends here.” It is used in other types of ancient mythology as in Babylonian tales of ten kings with fantastically high ages who ruled prior to the flood of Gilgamesh.
The idea that these stories are literal is a modern invention that exploded especially with Adventism which sees “time” as the constant for everyone, even God (which is where the Jehovah's Witnesses got it). This is contrary to both Judeo-Christian theology and science which teaches that time is relative.
*-While the stories of Abraham are not history in the strict modern sense, they are also not retelling his life through this same type of fable-enclosed literary garb.