"Vintage" (5+ years since the introduction of the hardware model) and "Obsolete" (7+ years since the introduction of the hardware model) are mostly relevant to the ability to obtain hardware service and repair parts.
How long you can keep installing new OS updates varies.
I'm using a Late 2009 iMac that originally shipped with Snow Leopard (Mac OS 10.6). It can run everything up to High Sierra (macOS 10.13). So it was able to run the most current version of the OS until September 2018 (when Mojave came out), and one of the "most recent three" until November 2020 (when Big Sur came out).
That's probably longer than you can expect from most Macs.
To take another example, a MacBook Pro (Retina, 15-inch, Mid 2012) that would have shipped with some version of Lion (10.7) or Mountain Lion (10.8) can run anything through Catalina. Catalina was one of the "most recent three" until October 2022, when Ventura came out. (It's worth noting that as of Catalina, Apple dropped support for 32-bit applications.)