I had couple of cats (orange male and tortoiseshell female) that lived 20 years after I picked them off the street. The female had only one kidney and the male had an extra vertebra but these things only became a problem in their last year.
They were both very calm creatures. The male was one of the most gentle cats I've ever known. I really miss him greeting me by nodding at me from the sofa when I got home.
Can you describe what the male looked like? I have a tortoiseshell who's all crooked. Her paws are twisted inward, her tail is shaped like a spring, her rear legs are longer than her front legs. She's all weird. Now I'm wondering if she has extra stuff like a vertebra too. Does your male cat looked overall normal despite the extra vertebra?