We had a Siberian Husky, Ana, who we had to put down shortly before we moved overseas when I was ~10 (fourth grade, I have zero idea of what age I would've been). She was getting really old, she was around thirteen or fourteen, and where we were going was a really hot place so it was fortunate that she wouldn't have had to endure it.
We also had a unfolded ear Scottish Fold, Tigger, that we had to put down on my birthday of I think freshman year of high school. His kidneys were failing and apparently this wasn't a new thing since a sign of kidney failure is a routinely having to drink water (more than usual), and as I remember of him, he almost always was drinking from the sink every time we were in the kitchen or passed by the kitchen.
We now have two Scottish Folds again, Maddie and Sirius, they're about six I think. They're doing well as far as I can tell. Maddie has an immune system "disorder" (I don't even know the technical term) in which her immune system is weakened, she also gave it to Sirius but his isn't as severe as her's (she has a regular cold basically). We give them steroids in canned food and they do okay. I really like Sirius so it's going to be really hard for me to watch him go....