See this Yalkut Reuvein at the fourth and fifth line, that brings a Pshat that Mesushelach dies 14 years after the flood. As far as I am aware this cannot be resolved with the timeline that exists in the Torah, if the years he spent in Gan Eden would be counted towards his age. The Yalkut must not be counting those years into his life.
However, in this article which sources Christian and other non Jewish sources, there exists other timelines that are different from our text in the Torah, and which would support the fact that he dies 14 years after the Mabul.
Can anyone source anything from a Jewish contemporary to support a theory that Mesushelach lived longer than 969?