I don't know if I should necro this, but this doesn't seem to be an overly active forum so whatever.

For me, on hardware front it's retro if the manufacturing had stopped at least 10 years ago. Usually it's about 10-15 years when the used hardware price hits its lowest for the high-end prestige products.

Regarding OS, if the developer ends the official support. Third parties drop it sooner since by the time most users move on to the current version.