oldest that I have owned?
the one I've lived in since 1990. Never thought we'd still be in it by this point.
the original was built sometime in the 50's, it's been added on to, we've done some stuff to it, but it's basically functionally obsolete.
cast iron plumbing in some places, old electrical wires, have replaced all the windows, siding roof, etc.
I've made some mistakes, but the worst was when we had it resided not to put up another 2x4 wall so that we'd have 8 inch staggered walls
it's a great location, good well for our area, but it's a constant headache.