Most Christians today ignore the fact that we have no idea how long it was between the creation and the time that Satan fell.
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None of that (the date of the earth) is actually important to me. I take the Genesis account as figurative with the understanding that Satan is 'the flesh'. The first thing that God did with Adam was establish language (by naming things), it wasn't long after that when flesh "fell" and became something that was more of an adversary than a friend. The flesh kept primitive man alive and 'blameless' in the past by our simple animal instincts and behaviors, now, with the power of cognition and inner dialog through language, we're both able to comprehend and connect to a higher principle as well as choose not to obey 'the voice of God', and boom: shame, guilt, corruption, is born, the fall of man, the fall of Satan, the fall of the flesh.
In my opinion, the story of Adam is the story of the first person capable of 'hearing' the voice of God which is a Spirit inside of us, the first person capable of disobeying this "Voice", and as such, the first person to disobey It, and feel guilty about it, and hide from It. The same story could have taken place on different continents, or could have spread from a single person. Adam is sometimes called the first Son of God... "For as many as are led by the Spirit of God, they are the sons of God." Then perhaps these "Sons of God" quickly intermingled with the rest of primitive man and the first civilizations came to be.
The Tetragrammaton (YHWH) is called "I Am" and "The One Who Is and Causes to Be"—the Judge—the Decider. And we are made in this Image. The spirits all come and talk to us and we hear their cases and decide what we're going to do in any given situation based on our very limited and corrupt knowledge, like judges. And there is a Holy Spirit in there somewhere—the Spirit that speaks the case of righteousness to our heavenly courtroom, that, if we listen, and think, and do what it says after hearing the case of the other spirits within our psyche, we can be righteous to the extent of our limited knowledge and understanding—what we are completely unaware of is not a sin in which we're personally responsible; like the animals. In that realm, the realm of general awareness of truth, we are subject unto higher powers—parents first, then culture and society and those influences, etc...
My off-topic ramblings for the night... apologies.