Needless to say, if age is what you choose as the determining factor
It should be clear from my posts that my reference is "of a kind or style no longer current". It never was a good match, but in the olden days the best choice. When the WSI/PSD chips came out specifically made to match the '51 the 8255 became obsolete. The came the HC/HCT chips and, suddenly, there was drive enough in the '51 to really do things. Later came the affordable (C)PLDs and now we have the 8 port chips/the 4 posr chips with sufficient internal memory. So the 8255 is 5 evolutions old and that makes it "of a kind or style no longer current"

One comment you made (I think that was you), indicating that the 8255 was designed for the 8031 with no internal memory ... is completely wrong
It was not me, my point is the opposite "the 8255 was not designed for the 8031" and thus present a sorry match to the '51.

Erik