Let's say someone possessed that mutation. You have to remember prior to 200 years ago, your chances of dying from a disease, an accident, hunger, race, religion would have killed you anyway.
Even today this is true, from different causes. If you eat too many cheeseburgers you die of coronary artery disease before you die of old age. Anybody can still get into a car accident or get cancer. Even minor injuries can result in infection or blood clots. Every meal is another chance to get food poisoning.
Maybe the people who don't age just died of something else eventually.
Maybe the people who don't age just died of something else eventually.