Only Christians regarded the earth was flat and was created few thousand years old. Scholars like Ibn Tayymiyah in 1100 BCE debated with Christians in past saying the earth is round and we do not know for sure when the heavens and the earth were created. On one of the sayings of prophet Muhammad (upon whom be peace), he said Almighty God wrote our sustannance 50,000 years before the heavens and earth were created. So to say God did not existed 30,000 years ago is simply a wrong statement.