An animal called a babirusa has a horn that can grow into its own head. It can be impaled with its own horn!
A babirusa is a member of the pig family. It has long canines that form horns that curve back towards its forehead. Most babirusas never grow large enough to have these horns pose any problem to them. However, on a rare occasion, a babirusa will grow to be old enough to have the horn grow into its own skull. The ingrown horn kills the pig.
A babirusa skull with an ingrown horn is a rare artifact. It’s absolutely incredible that a tooth could grow to the point that it could actually puncture the skull of its owner. For a biologist or a zoologist, getting a look at this self-impaled creature would be a treat. At least two fully intact impaled skulls are available among the scientific community for examination.
For this creature, old age might not be an advantage. With age may come wrinkles and white hair, but at least we don’t have to worry about killing ourselves with our canines. Our teeth would be more likely to fall out