John Hospers, first Libertarian Party presidential candidate, turned 91 on June 9, 2009. Other presidential candidates in the general election who lived at least that long include Strom Thurmond (100), Ronald Reagan (93), Gerald Ford (93), Frank Zeidler (93), Darlington Hoopes (93), Roger Babson (91), Claude Watson (92). Thanks to Darcy Richardson for that list, which may be incomplete. UPDATE: Darcy also notes Benjamin Spock lived to be 94, Barry Commoner is still living and is 92, and Enoch Holtwick lived to 91.
Hospers is somewhat famous for having received one electoral vote from Virginia, in 1972. He and George Wallace are the only actual minor party or independent presidential candidates who have received an electoral vote in the last 60 years. U.S. Senator Harry Byrd also received electoral votes, but he was never an announced candidate for president, even though his name appeared on the ballot in a few states in 1956 (Byrd got his electoral votes in 1960).
Zeidler and Hoopes were Socialist Party presidential nominees; Babson, Holtwick and Watson were Prohibition Party presidential nominees. Spock was the Peoples Party nominee in 1972 and Commoner the Citizens Party nominee in 1980.