We can’t know the date of Creation for sure, though there are some hints in the Bible and in Creation itself to give us a general number.
If you take all the ages of all the men when their mentioned son was born and add them up you get a time for Creation at roughly 4000BC. This is the youngest the earth could possibly be.
However, the odds of each child being born on his father’s birthday is slim at best, so we should add partial years into the date. But, you can’t stretch it very much without making the whole list irrelevant.
Many point out that the genealogy lists in the Old Testament, especially Genesis, are different than the lists in the New. They assume since the New leaves out names that the Old has, that we can add in several generations to both, stretching the age of the earth.
The problem is in the translating, though. You see, when the New Testament says “Abraham begat Isaac,” "begat" comes from a Greek word that means “is the ancestor of.” This can obviously mean several generations left out without calling the Bible a liar.
However, the Old Testament word translated into the English “begat” is a Hebrew word that means “he himself was the father of.” This cannot be stretched without destroying the integrity of the Word.
Where the Bible quits giving us ages at the birth of sons, it starts telling us the length of time each judge ruled, each king reigned, or the length of captivity by an enemy. Many scholars have added all these dates up and they all come to an age within just a couple of hundred years of each other (depending on the interpretation of a couple of scriptures that could mean different numbers. For example, we aren’t quite sure if God's promise to Abraham that his descendants would leave Egypt in 400 years should be counted from the time the promise was given or the time his descendants entered Egypt. Both views have valid arguments [though I lean towards it starting in the days of Abraham since the number of generations listed fit that date better]. This is a difference of about 200 years.)
So we could safely say the Bible says the world is around 6000-7000 years old.
Those methods of dating that tell us the earth is much older (on the order of 4 billion years) are all based on very flawed science and assumptions. There is no proof of an old earth. In fact, the decay rate of Carbon 14 should leave us with many fossils with no measurable carbon left in them if the earth is more than 100,000 years old. We have yet to find one sample without measurable Carbon 14. Thus the earth could not possibly be more than 100,000 years old.
The earth should reach Carbon saturation point (the same amount of carbon entering the atmosphere from the sun as leaving it) at 30,000 years of age. We have yet to hit saturation point. Young earth- less than 30,000 years old.
At the current rate of salt entering the oceans from erosion, the seas should have been too salty to support life millions, if not a billion, of years ago. Assuming the oceans started as fresh water (mostly) the current oceans have the salt of about 5000 years of erosion. The biblical flood would have happened 4,500-5000 years ago.
The mountains can’t possibly be more than a few thousand years old because at current rates of erosion they would have already been washed completely flat if they were very much older, certainly if they were a million years old.
If the moon and earth are both 4 billion years old as evolutionists say, there should have been 18 inches of dust when the astronauts set foot on the moon. There was only 1/8 of an inch.
The moon is moving away from the earth at the rate of about an inch per year. At that rate, it would have been touching the planet a mere 10,000 years ago. The moon could not possible be more than 6-7000 years old, and since it plays such a big part in the weather patterns and tides, life cannot exist on earth without it.
And ancient people records from cultures not currupted by the Greeks (who believed a form of evolution) put all their cultures as only a few thousand years old. No evidence for humans longer than that.
The one exception would be the Chinese whose direct history is 30,000 years old. But if you take a closer look, Their earliest records list kings who ruled for 900 years each. It's putting one king after another that extends their history so far. These long rules ended with the record of a great flood. It is much more likely to me that the "900 year rules" are instead simply the same overlapping lifespans listed in Genesis.
So, Tree ring dates, ratio of salt in the oceans, amount of erosion in general, ice flow dates, lunar dust depths, distance of the moon from the earth, and several other scientific measures tell us the earth could not possibly be more than a million years old and is closer to 10,000 at most, and in several cases, that is stretching it a lot. So we can put the Creation Account at 4000-5,000BC.
(See the many good books on the subject at the “Creation Research Institute” and “Answers in Genesis” for a more in-depth discussion on the science supporting Creationism and a young earth.)