I have a Mac Mini I bought early 2009. Still seems to work fine, though I admit I don't use it very often. I recently upgraded it to 8GB RAM - I just like upgrading computers! Bit fiddly to get it apart and back together but I found some good instructions (on YouTube, I think).
It wouldn't take the very latest software update - some weird excuse about the WiFi hardware not being supported. I wouldn't mind running it on wired Ethernet only, but Apple wouldn't allow the upgrade because of the WiFi.
It's now running El Capitan 10.11.6. I just switched it on to find that out and the clock was wrong at first - though it fixed itself once the Mac automatically connected itself online looked up the correct date and time from the internet. I guess the battery that keeps the clock running when it's off has died at last - I'll take a look at replacing that (or at least removing the old one) as old dead batteries, even the small ones, are notorious for leaking and destroying the circuit boards around them.