Young cats are frequently killed by cars. Photo by kitty.green66, https://www.flickr.com/photos/53887959@N07/
Another thing that kills older cats? Behavior. Of all the cats euthanized for behavior (43 of them, just a little over 1 percent of the sample), 42 were over the age of five (median age 16). There was no information as to whether those behavior problems might have been related to medical issues (e.g., a cat eliminating outside the box due to diabetes or cognitive disorders).
While the study did have some limitations, it did have a nice, large dataset with randomly selected records to avoid any potential bias or overrepresentation of particular veterinary clinics. However, people who didn't report a cat's death to a veterinarian are not included. Those cats who do not receive veterinary care may have had a different life span than those who do, or may die for very different reasons. This study also can't tell us that any specific cat will live longer, although there were some interesting patterns that tell us some generalities about the feline life span. The statistical model only explained a small percentage of the variability in the data, meaning that there are other important factors that may have been missing from the analysis, such as diet, outdoor access or vaccination history. And of course, as a correlational study, it cannot tell us what causes a long life span, only what factors might "dance" with it.