I have an old Thinkpad T23, it's about 15 years old. It can run Windows 7 (with aero off) perfectly well, and also stuff like Libre Office. Linux is not so good on it, due to having to play with the graphics drivers, which I've never really got working.

It all falls apart when you want to use the Web. A Thinkpad T23 with a Pentium3 CPU just cannot render Modern Websites at acceptable speeds.

Basically if it wasn't for heavy JavaScript websites, most people could still be using decade-old machines for their day jobs.