> the wide majority of owners will have had the unit for <5 years.

No one cares about how long you had the CPU in your possession, nor are we worried about the silicon expiring. If you restarted the factory line and got a brand new chip today, it would still be considered 5 years and 1 month old. Like finding a factory-sealed retro console.

> If the hardware can run just fine, what makes it old?

When something is "old" is context specific, related to how fast the world moves away from it.

To give some easily digestable examples:" A 1 year old person is very young, a 1-year old ant is very old. A 70-year old CEO is old, but might perform the best they ever have in their entire life. A 50-year old car is old, but fully compatible with modern roads and fuels (depending on spec). Despite no formal definition, these are quite objective in that no-one not playing devils advocate could possibly disagree.

For chips, they are old after 4-5 years because the chip world moves fast. This chip has been superseded many times (a great-grandparent at this point), is in the bargain bin as of late last year at somewhere between 1/3rd and 1/6th the price depending on ongoing sales as shops clear unwanted deprecated stock, and now does the work in more than twice the time and with more than twice the energy than the current product in its own line. No one would reasonably look at this side by side with the current offering and think "that's not old!".

(Note: Pre-Ryzen and Apple silicon, the "time to old" was longer because Intel's monopoly and laziness had caused complete stagnation within desktop CPU development, which is what we have grown sued to.)

Buying an old chip is done for the same reasons as buying an old car: If you don't really need it much, it also can't bring you a lot of value and so something something brand new won't mean much to you. Getting a bargain on something old and/or used is great. Whether it is a chip or a car, efficiency doesn't matter if its mostly off anyway. And just like any NES plays NES games as well as it did from day one, the old car if serviced still does the same job it did when it was new.

> It isn't "objectively" old. "Old" does not have an objective definition.

If you believed this, it would invalidate your entire line of argument that the chip (and your car) cannot be considered old as age cannot be classified and is irrelevant: considering the chip not old is therefore also wrong.

Considering that you are specifically attacking the idea of considering the old with the idea that their useful life should be longer, completely ignoring that I mention that devices can be used irrespective of their age, I do not think you actually believe that the age should not be classified. At the same time, if you did not think it was objective, your argument would have focused on saying it was subjective or context-specific rather than saying the classification was wrong.

> that perspective is consumerist, exactly what corporations spend lots of money to try and make people think.

That consumerism is also why the chip is a bargain and new chips are affordable, and the only argument for buying an EOL chip is price. Having any sort of used market for things that get better with time requires people to often buy new things and get rid of old things. Having new things be affordable for anyone requires a significant churn.

> a carbon emissions perspective ...

... is not relevant as I make it very clear that being old does not mean it needs to be replaced. Even if it ends its service life with you, a responsible person would sell it or give it away so someone else can use it instead of buying new.