Regarding the validity of the letters of Paul...
The earliest letters were written about 55 AD. So 55 years would have passed before Paul wrote down the stories from eye witnesses that may still have been alive. Putting aside the very obvious and serious problem that human memory is shit at that sort of thing, there's also the problem of life expectancy.
I'm still digging, but for Paul to have any chance of talking to any eye witnesses, life expectancy would need to be at least 65 (or thereabouts). A 10 year old would presumably remember the events but not their context, flow or significance. A 20 year old follower of Jesus would probably remember a lot more about how the events stitched together and their significance. The adult would presumably have a better chance of remembering the words Jesus spoke, but again, human memory is pretty shit, and nobody is likely to remember spoken words for 55 years (most people can't handle 5 minutes).
So anyway, what was life expectancy in the time of Jesus?
Palestine in the Time of Jesus: Social Structures and Social Conflicts By K. C. Hanson, Douglas E. Oakman has this to say:
Life expectancy: approximately twenty years for live births, and approximately forty years for those who lived past five.
Unreferenced though.
Evidence from the Neolithic in Orkney:
A neolithic tomb at Isbister (The Tomb of the Eagles) on Orkney, off the north coast of Scotland, produced the remains of 342 people. The age profile of the bones showed a population where children outnumbered adults three to one. The most common age of death was early adulthood, between 15 and 30. Only 1.5% of people were over 40, and very few lived to reach the age of 50. Old age, rather than life, began at 40.
Chalcolithic: ~30
http://sticerd.lse.ac.uk/seminarpapers/dg09102006.pdf
Bronze Age and Iron Age: 35+
http://en.wikipedia.org/wiki/Life_expec ... _over_time
So, if we assumed the highest estimate there, 40, was accurate. That sounds suspiciously like Paul didn't start writing his letters until after everyone who may have met Jesus first hand was actually dead.
