My oldest film camera is my Grandfather's Nikon FTN. When he purchased it new it was a Nikon F, and it had to be modified by Nikon USA to accept the FTN finder. As best as I can tell it's a late 1961 or early 1962 S/N.
I inherited it when he passed away in 1989. Early on I used it a lot as it was my only camera, and I took it with me everywhere. Today, if I squeeze a roll or two through it each year that's a lot. But I'll never part with it and I had both the camera and 5.8cm f1.4 Nikkor S lens refurbished in the last few years.
My oldest digital camera is an Olympus C-2020 that a friend gave me a long time ago. I still have a working smart card for it so I use it for 25 to 50 shots a year. For 2.1 Mpeg it still does a great job for pictures I want to post to the internet.
My most used older digital is a Canon EOS 1DMK2. I shoot mostly nature and wildlife pictures. I have several newer Canon cameras with greater resolution, but it just works no matter what I do with it. While it is only 8.1 Mpeg, and I can't use more than ISO 1250 with it and get an image that I can process due to noise, I still use it quite often. Paired with a Sigma 150-600 lens it nails focus with more accuracy than any other newer camera that I own. For that alone I find it difficult to part with.