Apple has support statuses for discontinued products which kick in five years ("vintage") and seven years ("obsolete") after the it stops being sold.
It's disingenuous for Google to start counting when the product is released. As the buyer, I don't care when it was released, I care when you sold it to me as new. I could buy a Chromecast Ultra (the current-generation 4K Chromecast, released November 2016: https://store.google.com/us/product/chromecast_ultra) and, by this standard (which may not even apply to Chromecasts, FWIW), they could discontinue it and drop support for it tomorrow.