i figure that big bang is what happened when God clapped his hands and those seven days well lets just figure since God is eternal his measurement of one day is probably a bit different than ours. besides whoever wrote Genesis may not have be particularly good at math, y’never know.
Moses penned Genesis on instructions from God.
And, yes, the Earth was created long before the events written of in Genesis as it and other parts (OT and NT) of His word would attest.
Young Earthers are good, but misguided, folks.