If there was ever a time when nothing existed then there would be nothing still, because nothing has no potential to become something. Out of nothing, nothing comes. And yet there is something, so we know there has never been a time when nothing existed. Something has always existed. What is that something?

Could the universe be eternal? No, as evidenced by the thermodynamic properties of the universe. The energy in the universe is finite and increasing toward entropy. If the universe were infinitely old, we would have reached a state of entropy an infinite time ago. And yet we have not reached a state of entropy, therefore the universe is not infinitely old. It began to exist a finite time ago.