Does the Bible, from a conservative Christian perspective, really say that Adam and Eve only lived about 6000 years ago?
The fact is, the Bible doesn't make any explicit statements about the specific age of humanity (or of the earth or universe either). All we have to go on is the record of nature (general revelation) and inferences based on what the Bible does say. So, why would some Christians make such a claim that seems to fly in the face of established human history? For that, we need to hear, "The rest of the story..."
The roots of this go all the way back to 17th century theologians, Ussher and Lightfoot, who decided to calculate a date for the creation based on the biblical accounts. They arrived at a date of around 4004 B.C. based on their reading of the genealogies found in the Bible. Because this chronology found its way into early versions of the King James bible as headings, it has become widely accepted as "the biblical timeline" for many Christians.
However, there appear to some serious problems with this approach. First, most conservative biblical scholars, who have studied the issue, acknowledge that the genealogies in the Bible and other ancient cultures were often "telescoped". Telescoping involved including only prominent names in a list, instead of exhaustively including every name. The reasons were many, but included: establishing royal lineage, having a certain number of names in the list (like 7, 10, multiples of 7, etc.), or even for aesthetic reasons. Unlike modern genealogies, these genealogies were never intended to serve as strict time lines or as exhaustive records of ancestry. At best, these genealogies give a lower limit on the time frame. I believe that that is what Ussher's chronology gives, an estimate that humanity was around at least from about 4000 B.C. onward.
So the real question is, can we estimate how much telescoping exists and what is a reasonable estimate for Adam and Eve's time on Earth? Several people have recently attempted this (see http://www.reasons.org/files/non-staff-papers/The-Genesis-Genealogies.pdf and http://www.reasons.org/files/ezine/ezine-2010-04.pdf ). They have concluded that a range of 40,000 to 100,000 (+/- 20,0000) years ago is possible, based on close examination of the various genealogies. This agrees closely with various DNA studies that also have provided evidence for the ancestry of humanity in that time range (Y-chromosomal Adam and mitochondrial Eve). In addition, it agrees with the timing of humanity's "cultural big bang" around 40,000 years ago and evidence of Australian aboriginal migrations around 50,000 to 70,000 years ago.
On a related note: I believe that Adam and Eve were real individuals specially created by God in His image. He gave them "the breath of life" that was distinct from any other creatures, including the modern primates and extinct hominids. While animals like birds and mammals share some form of mind, will, and emotions with us, only humans have a spiritual nature. In addition, only people create and appreciate art and jewelry, contemplate our future and life after death, have the ability to commit evil and recognize right and wrong, and imagine a creator God who transcends our immediate existence and experience.