Historical Evidence: http://www.agapebiblestudy.com/documents/Historical%20evidence%20on%20the%20exhistance%20of%20Jesus.htm
Your assertion regarding the date of the New Testament is blatantly incorrect.
We have good reason to believe the Gospels were written by EXACTLY those whose names are attached to them.
The oldest New Testament fragment, known simply as "P52" (or Papyrus 52) dates conservatively to sometime between 115 AD and 138 AD. Some scholars would place it even earlier. This fragment preserves a bit of The Gospel of John. Copies of other books date to the second century as well.
Also, we know that the Gospels of both Luke and John were already attributed to as such as early as 170 AD. This is thanks to a rather interesting document known as the "Muratorian Fragment". In it, a church leader is discussing which New Testament books were considered cannon by his church. While not identical to the modern NT cannon, it does display some of the criteria that would be used to decide which books were canonical and which were not by the early church.
The Muratorian Fragment is referred to as a "Fragment" because we don't have the entire document. He refers to Luke as the "third book of the Gospel" and John as the Fourth. We don't have his entire reference to the second book, but the fragment does preserve the information that it contains Peter's recollections. Since John Mark (the author of the Gospel of Mark) is known to have been Peter's personal scribe, and since other church leaders of the same era stated that Mark wrote his Gospel based on what Peter had taught him, it is safe to assume that the original Muratorian document preserves the author of Mark as well.
Thus, by 170 AD, the Gospels had been around long enough that they were already in widespread circulation. In a world without printing presses, where every document had to be copied by hand, and where only professional scribes could do such a thing, and where few scribes would have dared copy Christian books under threat of death from the Romans, the books simply MUST have been composed at the very beginning of Christianity.
I have done a great deal of research on this, and your claim simply doesn't hold up. Certainly other skeptical scholars have made this claim, but the evidence is against them.
Irenaeus of Lyons is the person that skeptics often claim "attributed" the Gospels to the authors Matthew, Mark, Luke, and John, but this simply isn't the case. He merely related what they Church had always known, and what he personally had confirmed from the likes of Papias and Polycarp (who was a personal student of The Apostle John).
One thing that is important to note. While it is true that the earliest copies (which date to within decades, not centuries of their composition) do not bear any names at all, once churches began to attach names to the documents, they all attached THE SAME NAMES!!! All over the Roman world!!
Now if, as you assert, the names were later attributions, what we would see is that different churches would have attributed each Gospel to a different person. Remember, these folks did not have the internet, or even telegraph wires. There was as yet no central authority that could say, "Attribute the first Gospel to Matthew," and make it stick. For crying out loud, why would you make up the fact that the first Gospel comes from such a minor apostle as Matthew? If he hadn't written the Gospel that bears his name, you wouldn't even know who he was!! If you were going to make up names for the Gospels, you would attribute them to Peter and James, not Matthew, Mark, and Luke.
But yet, as the churches began to label the Gospels, they all labeled them exactly the same. And church fathers across the empire all give the same testimony as to who wrote each.
So yes, we DO know who wrote them. This information dates back to within decades of their composition. The claims that the names were attached later simply don't hold up to scrutiny.