While medical technology has gotten a lot further, the amount of things that can kill a person, not just render deadish, has increased immensly.
There is a disease where a tumor grows within the brain and targets the memory part, and slowly certain memories just disappear. Even long term stuff. You still have vague feelings of memories sometimes.
Most people have the lifespan of us here on Earth, a little longer; around 120 years. But a select few, "Semi-mortals", can live to 500 and beyond. It isn't *exactly* genetic; you have a higher chance of being one if your parents were one, but they are still very uncommon; one in 1 billion or so. These Semi-mortals are more resilient; they are more resistant to diseases and bodily damages compared to humans, and they heal faster. Many Semi-mortals do not know what they are until they get seriously injured, or question why they don't get sick.