16All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness, 17that the man of God may be complete, thoroughly equipped for every good work.Why must you speculate about something that is omitted from scripture ? There is nothing to confirm this speculation in the NT, there is nothing in God's plan of salvation that requires it and there is nothing this speculation answers.
I personally believe in this gap theory. But this is not a big deal either way. I may be wrong, but it does not matter, and if i am right it does not matter. Our story starts in the garden of Eden with Adam. The fall, Gods prophetic covering of the two with the animal skin to signify the coming Christ who would cover all sin. You can interpret scripture to both cover the gap theory and to also intepret a younger earth. I believe we will have all of eternity with Christ to learn all of these things.