The oldest is Methuselah, who lived to 969 "years," which I believe to mean cycles of the moon. If you divide 969 by 13, the number of lunar cycles in an actual year, you get 74.5, which would be a nice old age indeed back then!
The hebrew word for years is shaneh, which can mean a number of things:
a) as division of time
b) as measure of time
c) as indication of age
d) a lifetime (of years of life)
None of these definitions are "the amount of time it takes for the earth to revolve around the sun," leaving a lot of room for interpretation as to what the word actually means. Granted, these people were barely out of the Stone ages, so what better way to count the time than the cycles of the moon? It seems to be the easiest way because it is so short and easily counted.