I know, I know, there are better paradoxical questions than this. For example, "Can he create a box that he can't look into?" and "Can he create a round triangle?"
People are constantly trying to come up with these mind-bender questions that disprove God's infinity, but we have to point out that they make no sense in this finite plane of existence we dwell in. First, we have to point out that there ARE infinities outside of theory. For example, how short is NOW, as in the point of time, right now, between the past and the future? That's right, it's infinitely small. Now answer this question: By math definitions, a ray goes infinitely in one direction from a point, and a line goes infinitely in BOTH directions from that same point, but which is longer? See what I mean? There ARE infinities present in our world, but our finite laws can't account for them.
Besides, such questions merely stress and confirm the point that there is no power greater than God, so much so that one is forced to pit God against Himself in order to find His equal.
Another case against God you might hear is that God can't be omnipotent (all-powerful) if he cannot change the future, and he can't be omniscient (all-knowing) if he can. But this one isn't hard to debunk either. An all-knowing God would foresee from the beginning a time in the future when things needed to be changed and would change it from the beginning. Some might argue that this would cancel out man's free-will, but as shown in the article, "Why did God create unbelievers?" man's free-will and God's fore-knowledge can definitely exist together.