Time and again the question about the "oldest pixel font" crops up.
I went digging a bit.
Pixelated lettering sure is old. You get mosaics in ancient cultures. But what about fonts? I'm going to go out on a limb here and propose that embroidery alphabets published as specimens for embroiderers should be considered fonts rather than lettering. The grid-bound specimens effectively constitute patterns of rules and instructions to be executed (albeit by humans).
Given this definition (which is probably debatable), below are the oldest "pixel fonts" that I've been able to find so far. These two cross stitch alphabets were published in 1533. 476 years ago! Machiavelli's "Prince" had just been posthumously published, Luther's Bible was about to follow, Da Vinci had recently passed away, Michelangelo was alive and working, movable type was still a young technology, and the New York area had just been discovered by the Europeans.
These two alphabets were included in Livre nouveau dict Patrons de lingerie, edited by Pierre de Sainte-Lucie, published between 1530 and 1533. The alphabet of roman capitals (of which, unfortunately, I only have a cropped image) was apparently previously published, in a slightly differing form, in a book by a certain Schönsperger in 1524. The author of the book I got this from (Catherine Pouchelon, Abécédaires Brodés) maintains that that was the first cross stitch alphabet ever to be published.