Yes, science is different from religion. Science makes its claims based on observation of the universe. The age that scientists have for the earth and also for that of the universe are not simply made up numbers or simple pronouncements. It has been arrived at by a study of the evidence presented in the natural world: Rocks, stars, planets, animals, plants, the oceans, the ice, etc. The claims made in the Bible, Qu'ran, etc. are not based on such evidence but on tradition, that is the difference. Ussher got his dates not by studying the real world around him, but rather by taking the the known historical date of the fall of Jerusalem to Babylon and then adding up the numbers of the ages of the patriarchs found in the Bible. One date was based upon a study of the actual physical world and evidence we have plainly in front of us now, and the other was based on calculations made from a book of tradition. This is a basic fundamental difference. And further, the scientific dates can be questioned when someone comes up with better data, this makes science superior to scripture as science can change when it figures out its wrong and strict adherents to scripture end up clinging to something long shown to be factually in error. Eventually scientists may find a different age of the earth and the universe (they are separate things with separate ages), but it is not going to be anywhere approaching 6000 years, I guarantee you. The evidence totally points the other way. It would be like trying to plumb the depths of the ocean and declaring that it must be six inches deep because you had a book your mom gave you that said so.
As far as the whole "nobody knows anything" goes, if you take that very far it becomes extreme. The histories of ancient Sumer and Egypt are well established in their records and backed up by physical archaeology and carbon dating to well beyond 2000 BC. We have the kings lists for all the Egyptian dynasties and the Sumerian dynasties as well. Just because nobody is alive today who was alive in 2000 BC doesn't mean we can't have a decent idea of what was going on back then. Nobody today is alive who was also alive in 1880 AD either. Does that mean we know nothing about 1880 AD? This is like saying that the Wright Brothers couldn't have invented the airplane in 1903 because that was before "the flood" or some other event that destroys and remakes the whole earth, yet we have the airplane in use today and all of the writings point to that occurring. I used to amuse myself when I was a kid with the thought that the only thing real in the world was probably my local area and that far off countries like Japan and China and England were probably just made up stuff. After all, I had never been over there to see them. I realize that the mountain of evidence shows that these places are indeed real, so this amusing notion I entertained is implausible. If you really want to accept something like this, why not believe that the world is only a day old and that we were created last night along with all of the false memories of our lives? It's certainly a simpler explanation.
If you want to claim that modern humanity started with 8 people around 2000 BC, then you have to explain how the world could have been completely populated and established civilizations each with their own very very different traditions within only a few hundred years or less. You need to come up with a decent explanation as to why the Biblical chronology is at odds with the established historical timelines of other civilizations, and you need to come up with an alternative chronology for those civilizations that explains the discrepancy and fits their histories, and the general history of all non-Israelite people (Including the indigenous people of Australia and the Americas), into that Biblical timeframe and the generations of the nations mentioned in Genesis. This is what I meant when I said that I haven't seen any creationist adequately address this.
And this is only from the historical perspective. It is even harder from the biological perspective to seriously entertain the population growth figures, especially in pre-modern medicine society, necessary to repopulate the whole earth (including Australia and the Americas) from 8 people from 2000 BC in a way that is consistent with known population levels in various parts of the earth at various times (The Romans did take censuses and we have a general idea of the actual population of the city at various times during the Empire). I suppose if you think people used to live to be 900 years old (and even to 200 years old for the first millennium after the flood, in spite of the evidence from human remains of the period that show people were lucky to live to 40 back then) then they could have a lot more kids. An even more colossal problem from the biological perspective is trying to figure out how the world, being stripped bare of plant and animal life in 2000 BC, could have made such a dramatic recovery by now from a single seed point and spread over the world in their current patterns in such a short time.
) But that doesn't count obviously for the discussion in hand, since that , if anything, the Mids would be older the kingdom of Queops ( and if the Mids were made with stone taken out of the Sphinx pit as it is widely believed, they have to be older , since the Sphinx itself has serious rain induced erosion ).
) Preferring to believe alternative hypotheses becomes an act of believing in very very unlikely scenarios. There's nothing wrong with that, but it's not a scientific way of going about things.
Not that this forces a round Earth ( it can be only locally convex ), but definitely excludes a flat Earth 
