I had to put my 18 year old cat to sleep about a year ago. He didn't look or act sick, but had major kidney problems as well as what I am sure was diabetes at the end as he was always drinking and I was going through kitty litter like crazy.
My second cat I had to give away as my 2nd husband's cat allergies were getting much worse ( as in needing inhalers worse) She too is now gone on to kitty heaven. Just went to sleep and didn't wake up, according to the people who had her.
The older cat I'd had for most of the 18 years of his life, he was a "talker" and definitely a lap cat. He saw me through the loss of my first husband and always met me at the door when I came home from work.
The younger one was a very feisty, yet friendly cat and was about 9 when she past away this past fall.
I miss them both very much as they were family when I was single.