Depends very much on the 80 year old in question! My mother is approaching 80 and is quite rational and able to figure things out for herself, however, she is afraid of "breaking" technological stuff. Rotating volume controls and tuning are ok; push-buttons and menus (i.e. anything with a hint of built-in intelligence) are definitely not ok. That's probably not much help!
Knobs and switches with single, labelled function are ok.
Anything that requires the grandkids to fathom it is not ok