why is my cat who just turned 13..

Brief：
Answers: Incontinence.poor kitty. He doesnt mean to! i dont know but you can cure it by holding the cat by the tail and stomping its freakin head Inco.. 

However, this may not be the only problem. Do you clean the litterbox frequently? Some cats do not like to use dirty litter, and so will go elsewhere - and, yes, they can develop these habits in the middle of their life like your cat.

Also, cats are very sensitive animals and can become stressed terribly easily by the smallest changes. We have had cats come into the vet due to the fact that they were urinating through out the house simply because the owner bought a new set of furniture! Has anything changed in your house lately? Any new additions to the house - human or otherwise? Has there been any arguing in the household? These are common stressors.

Your best bet would be to collect a fecal sample and bring it in to your vet, along with the cat. The vet should certainly be able to help you, whether this is a physical or mental issue. Something is wrong with him physically. Get him to a vet right away.

Cats often do this when there is something wrong and they want to call your attention to it. Animals learn amazing things by sniffing each other's feces and such - they can often tell what's wrong with another animal this way. By not using his litterbox, he's trying to get you to smell what's wrong with him and fix it. He trusts you to do this.

Thirteen is not old enough for a normal cat to be suffering from incontinence, so this alone is not an explanation. Pay attention to other signs he might be leaving you - measure his food intake against the norm for him - have his sleeping habits changed, or the places he chooses to sleep? When something is wrong, a cat will often sleep in a place where they feel nothing can sneak up on them - they know they might not be alert enough to protect themselves in a hurry.

Get him to the vet - he's literally begging you to make this all better. Dementia and incontinence could be a health issue like others have said, constipation or other stuff

Litter box issues- you need to be sure the box is scooped at least once a day. And changed out completely before it gets smelly and reeks of ammonia.

If you changed litter types/brands recently he'l letting you know the new stuff just is not his style.

13 is old, but senility is not usually coming in til a later age.