Margaret,maybe this is something the vet can treat.
Yes seventeen is older,but many cats live okay longer.
I currently have four kitties that are seventeen or older. Three have slowed down but are active, pain free, and eat well.
The fourth one is very active and seems much younger.
I had one kitty live to be 22 and be healthy until about the last few weeks of her life.
Please wait and see what the vet says. Maybe it's treatable!