God might be larger and older than the Universe , we do not know that the Universe is infinate , neither scripture not science claims this. What God is made of is a total mystery ,what the Universe is made of is 60% a mystery.
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God might be an old man with a white beard dressed in Hebrew Rabbi's robes. God might resemble the Flying Spaghetti Monster or your mother, but what are the odds?
Most scientists agree that the universe, for all practical purposes, is indeed infinite, having neither center nor edges. It is made up of lots of empty space, matter and energy, some of each of which are of unknown forms.
Either God has always existed, or you will have to assume that he was created by something a lot more complex than life was. I don't see any alternative to these two hypotheses.