“Could the ages listed prior to the flood contain the month of death also?
1000 = 100 years and 0 months
965 = 96 and 5 months
Then after flood the month was dropped”
This is an interesting question and, as far as it goes, an ingenuous attempt at solving the perceived problem with the ages recorded on the individuals in Genesis 5. The oldest person mentioned, Methuselah, is recorded to have lived 969 years – far beyond anything recorded in modern history or deemed possible by our understand of human biology. So people have often suspected that these numbers might represent something other than the actual age of an individual.
The solution proposed in the question is that the age recorded includes the digits of the number of months. There are two problems with this proposal. Firstly, if the writer had meant to represent both years and months I think we might have expected him to say so. Secondly, and more fatal to this proposal, the writer did not represent these years in digits (e.g 100 years) but in words (e.g. one hundred years).
However this solution has somewhat in common with a solution speculated by Kenneth Kitchen. He notes that Sumerian king lists you find very large reigns (e.g. Alulim, who is recorded as reigning 28,800 years). It has been suggested that these reigns were exaggerated by the scribes by a factor of 60 and of 10 (the Sumerians had a sexagesimal number system). For example, it is proposed Alulim actually reigned 48 years. Kitchen proposes that something similar may have occurred with the numbers in Genesis 5. He suggests that the actual ages may have been exaggerated by a factor of five as when one divides the ages given most result in plausible ages when divided by five. (On the Reliability of the Old Testament, 446). This solution is not without its problems and still gives very high average age of death, but this proposal might indicate that we are missing some piece of information about the way ancient peoples used numbers.