KDE Plasma has been reported to work well on computers up 15 years old, and other FOSS projects run on devices even older than that!
At our stand in April at the Umweltfestival, we had a Dell computer from 2003. Debian with LXQt ran on it, but the BeOS-based Haiku ran even more smoothly ... and many KDE apps have been ported to Haiku. So we could demo GCompris to families with kids on a device that is 21 years old.
That is the power of transparency and user autonomy!