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I'm really not so concerned about when life may or may not have been able to develop during the 15 billion or so years of the universe's existence, so I'm not making any "common error". Besides, you're talking about things in strictly theoretical terms, so how could I be in error even if I did assume that life could have developed elsewhere 10 billion years or more ago? No one knows one way or the other on that count. Besides, you're talking about conditions making development of life as WE know it possible. Who knows what else might have cropped up?

The assumption that life has been around elsewhere for 11 billion years, or 15 billion years, 4 billion years, or whatever, makes no difference to what I am saying. And that is that 1) the odds of our having been noticed, much less visited, by another civilization in the 70,000 or so years of human existence, or in the 107 years since we started generating signals that might be detected beyond the bounds of our own planet, are incredibly small, and 2) that there is still NO credible, concrete, scientifically verifiable and conclusive evidence proving the existence of aliens.

Sure, we could be the leading edge of the development of life in the universe, but that misses the point I am trying to make. Whether I allow for the possibility of life being able to develop any sooner than it has here or not doesn't change things in any significant way.