I echo what the others have said, the going on the carpet is a strong suggestion of a urinary tract infection. I don't know about senility in cats, but I do know that when the elderly get a urinary tract infection, they can become very, very confused. When I was working at the nursing home, very often abnormal behavior was the first sign of a UTI in the resident.
Your Minnie kat sure is beautiful. Hope you can find out what is going on.