Among the oldest, no surprises to paleo/ancestral/traditional:
American bison---8,000BC
pigs, goats & sheep---7,000BC
lard---7,000BC
cattle domestication---6,500BC
milk & yogurt, & sour cream---5000BC
...but at the other end, these foods were older than I had expected, still over a thousand years ago (!):
loquats & flower waters---10th century
cod & nutmeg---9th century
spinach & sago---7th Century
eggplant---6th Century
pretzels---5th Century
lemons ---3rd Century
costmary & blood as food---1st Century