And who's to say the world isn't only 5 seconds old, formed with all appearances of it being old including all "memories?" That is equally plausible, but both ideas are useless and (sorry, but I can't help say this) insane to believe.
Both ideas do not offer any mechanism for how the world appears as it currently does, and even assuming they were absolutely true, it would make no difference -- If all evidence points to the mechanism of evolution to bring about diverse speciation in this planet, and a big bang starting the universe 14 million years ago, and these are able to explain the universe we see today as well as provide predictions about how it will be in the future, then it would not matter if all this data was "faked" 6000 years ago, or 5 seconds ago, we should still hold to these theories (old-universe) as true since they would not be violated.
The 6000 year old earth/universe theory should not be treated with anything other than pity and the response is patient education (not yelling, calling names, or most of the other responses). The scientific method has changed over the years - for many branches, we can not setup a controlled experiment to setup a hypothesis. We can only take data, and analyze it. (Ecology, star formation, development of flight in dinosaurs, and others.) This does not make unfalsifiable ideas equal to all other ideas.