I mentioned this in #dri-devel when I talked to the Mesa developers: They should decide on a number of years where it is acceptable to say "that's too old".

Not sure what number that would be. I too doubt that anyone is still using a 32-bit computer that's more than 16 years old today. But you have to draw the line somewhere. 5 years? 10? 20? I think 10 would be a reasonable number, but that's just my humble opinion.