I remember one of the last times I took my Monstrose to the vet. He was 20, and the vets and techs ended up standing in the doorway of the exam room to get a look at him. I heard someone say "That cat is 20 years old!!" He didn't look a day over 10!!
I love seeing old animals too! I agree it's rare. So few live so long, and in the same home.