The oldest of my current crop of kitties is 20. He's got some medical issues (chiefly diabetes which just developed a few months ago, and he's never been overweight). But he doesn't seem to mind his twice daily blood glucose testing and insulin shots, nightly subcutaneous fluids to keep him well hydrated, etc., and loves his very custom-made food. He feels fine and is having a grand time -- and doesn't seem the least bit concerned that keeping him that way is practically a full time job for his devoted human :-)
I know what you mean!I once had a vet from a veterinary school ask if he could use my cat family as a field trip for his students ... at that time we were dealing with diabetes, hyperthyroidism, skin cancer, kidney failure, and glaucoma.
Alas, all of those precious feline friends have now passed on ... we still miss each and every one of them.