Since I passed on some 1830s & 1840s editions to my sister (they belong to our mother, & I was just taking care of them), I don't think I have anything older than my early 1930s Larousse, bought new by my grandmother.
I have lots of electronic facsimiles of older books on CD & HD, though, back to the C16.
Damn! Just checked Arthur Young's Travels in France (PDF) & found it's a 1909 edition, re-edited, not the original from 1792 & 1794.