The oldest living former Met is none other than Yogi Berra, who supposedly once said "You should always go to other people's funerals; otherwise, they won't come to yours." Yogi turned 82 in May -- he played in 4 games (2 hits in 9 ABs) for the Mets in 1965. The other former Mets still living and over 80 years old: Duke Snider (who played more games in the OF for the Mets in 1963 than anyone else that season, and had a pretty good year) and Joe Ginsberg (for the Mets: 5 ABs, no times on base). Former Mets born before Yogi but who have passed away: Warren Spahn (1921-2003), Gene Woodling (1922-2001) and Gil Hodges (1924-1972).
I did this research using the baseball-reference.com PI Batting Season Finder http://www.baseball-reference.com/pi/bsl_finder.cgi, setting League to NL, Team to Mets and Sorted By to Year of Birth (ascending order) . Then I clicked on the earliest born players to check specific birth and death dates.