We have a cat that is 13 years old. He likes peeing in the house off and on, usually on blankets or in the dog cage. He does not do this all the time. We do have 4 cats in the house but 5 litter pans ...
Since none of us are vets, we can only speculate. Going by the symptoms you describe and your cats age kidney failure and g.i. lymphoma should probably be considerations.
As a side note, have a good friend whose cat was diagnosed and treated with low grade gi lymphoma over 4 years ago, still doing great and in remission.