I still run, and am writing this from, a 16-or-17 year old Dell E6510 (i5-540) that serves as my "around the house" computer. The battery life (with a huge 9 cell that protrudes out the back) isn't great, and it's hot and heavy, but with 8GiB of RAM and an SSD it works pretty well on Trixie with Cinnamon. My main machine is a 13 year old Lenovo y510p running Debian and KDE. You'd be hard-pressed to tell that it's any…
As now, there is a very wide performance profile for machines around then. From sub Ghz Celerons up to 3Ghz plus dual core things.