I would think that the technology for cryo freezing people would have been newish by 1999, so there probably aren’t too many people from before then who woke up in 3000. There may have been a few people who froze and unfroze around the same time, so he may not be THE oldest, but I think that he’s the oldest person in the series
Pauly Shore was born in 1968. Fry was born in 1974 according to the Infosphere.
Fry would likely have had knowledge if Pauly Shore was frozen before him.
My guess is a toss up between the 80s guy and Pauly Shore.
Edit- Since 80s guy died from Boneitis, Pauly Shore is the oldest. (Not counting the heads in the jars).
If you do count the heads, is anyone older than George Washington?
Infosphere and Fandom wiki both say Ben Franklin (born 1706) is the oldest known head in a jar