The impossibility of a past infinity has never been proven. It is counter-intuitive but can't be logically deduced without assuming the conclusion. I'm agnostic about whether it's possible. From my point of view, theologians tie themselves in knots over this seeming paradox unnecessarily. Zeno presented us with paradoxes, but the paradox doesn't actually keep us from overtaking and passing the slower runner or keep the arrow from reaching its target. The paradox of an infinite past never catching up to the present may be similar in nature. Even if time is past infinite, there has to be a present time somewhen, right?
I'm not anti-Christian. I'm anti-stupid.