I have an Asus ROG laptop I bought in 2013 with a 3rd gen i7, whatever the gtx 660 mobile chip was and 16gb of ram, it’s definitely old by any definition, but swapping for an ssd makes it super useable, it’s the machine that lives in my garage as a shop/lab computer. To be fair, its job is web browsing, CAD touchups, slicing and PDF viewing most of the time, but I bet I could be more demanding on it.
I had been running mint w/ cinnamon on it before as I was concerned about resource usage, was a klipper and octoprint host to printer for a year and a bit. Wiped it and went for Debian with xfce becauae again, was originally concerned about resource usage but ended up swapping to KDE and I don’t notice any difference so it’s staying that way.
I really hate waste so I appreciate just how useable older hardware can be, Yeah there’s probably an era that’s less true but I’ll go out on a limb (based on feeling only) and suggest that anything in the last 15 years this’ll be true for, but that’s going to depend on what you’re trying to do with it, you won’t have all the capability of more modern hardware but frankly a lot of use cases probably don’t need that anyhow (web browsing, word processing, programming, music playback for sure, probably some video playback, pretty much haven’t hit a wall yet with my laptop)