Welcome Brian! Do you have fond memories of your grandfather playing this accordion? Pray tell!
It’s difficult to say exactly how old this accordion is. I would say “circa 1930s” or “early 20th century”. Maybe someone on here can be more specific. Among us accordion nerds, we would say you have an “eight bass, two row, diatonic button accordion.” This means that each key will produce different notes (or chords) whether the bellows are opened or closed. These were produced by the hundreds back in the day, mainly for use in playing traditional or folk music in two or three musical keys. Hohner was a good company, and its instruments were solidly constructed. Unfortunately because these accordions are so old, many are in need of repair to be useful, although many others still play reasonably well. It’s a crapshoot. Because of the repair issue, many of these have a higher value as a beautiful and attractive collector item than as a useful musical instrument. Value (for me, in my location) would be about $50 - $250 wholly based on condition of the accordion. Good luck!