There are two basic reasons why I am not a young-earth or young-universe creationist. One has to do with Venus, which is ballpark for the sort of age estimate which Bishop Usher favored, i.e. 5000 - 10000 years more or less. We all know what Venus looks like now, 900 F surface temperatures, no regolith, statistically random impact crater dispersal, 90-bar CO2 atmosphere etc. etc. i.e. a vision of Dante's inferno.
Since Earth and Mars do not in any way look like that, you have to assume they are significantly older. Probably not hundreds of millions or billions of years old, but older than any sort of an age you could deduce from biblical chronologies.
The other reason for rejecting young-universe creationism is philosophical. Basically, if an omnipotent God figured out it would be a cool thing to do to create the universe 7,000 or even 17 billion years ago, then why didn't he figure that out 17 trillion or 17 quadrillion years ago? That does not make sense.
Without a time machine there's no real way of knowing but, until somebody produces the time machine, I am assuming that the universe is eternal, and that creation stories generally refer to the creation of our own Earth and local solar system environment.
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