Do you have a source for these life expectancy rates?
I will get them for you if you remind me... I read them from a chapter reprint of a book a friend at work gave me, but I forgot the name of it. The book actually had a fairly communist slant, but this chapter -- a slam on the industrial revolution -- inadverdantly cast the middle ages as nearly idyllic.
If you do a Google search on the term "life expectancy England 1200", it appears that the average life expectancy of a landowning male in 1200 would be about 31 years.