Also, concertinas might be small, but that doesn't mean they are cheap.
from the first half of the previous century; an accordion from 1829 by Cyrill Demian (that's the year it was invented, or patented at least) would be worth quite a bit even if it was completely unplayable, but even for an instrument from around 1900 you couldn't count on that (unless it is a really nice mantle piece, of course).
If the accordion is not in a good condition, one should probably deduct the cost of the necessary repairs from the value of the accordion.
Collin Dipper's instruments are quite ok again: he's got a waiting list of about two years! Oh, and it should be a full size instruments, of course.
As for bandoneons, I am not really familar with those; _the_ brand seems to be Alfredo Arnold, and then specifically the ones that were made around 1925. Finally, the value depends on the size and the possibilities of the accordion.
By itself the age doesn't matter, but for one thing: accordions have become better over the years.
But apart from maintenance and retuning, accordions can easily last 20 years.1931: In the middle of the century’s biggest accordion boom with hundreds of accordion orchestras, HOHNER founds the HOHNER Music Publishing House, the DHV (German Harmonica Association) and the HOHNER Conservatoire.1956: Giovanni Gola becomes head of the accordion department and sets new standards in the high-end premium segment.The exciting story of Matthias HOHNER, his rise to fortune and the assimilation of his numerous competitors is all documented in the main museum building.Special exhibitions are shown on the new premises a short distance away in Bau V, a huge former factory building on the original HOHNER factory site.4.000 employees produce 20 million harmonicas per year.