I'm honestly kind of freaking out about growing old. My great great grandma had Alzheimer's disease,…

I'm honestly kind of freaking out about growing old. My great great grandma had Alzheimer's disease, my great grandma didn't, my grandma is 52 and already showing signs of deterioration, my mom is still doing fine, so I'm really scared that it might be skipping generations. Idk if that makes sense and it might be an irrational fear, but my memory is already very very bad and I don't ever want to forget my baby or my fiance.