I'm pretty sure that Apoptoxin 4869 is something along the lines of a DNA rewinder, if you can call it that. For many, it completely kills all DNA cells, which allows it to be a very instant and fatal poison. However, for some who have a gene mutation, or the likes of it, will undergo a phase of partial telophase (something along the lines of DNA rewinding? I have no detailed idea about DNA processes, but I'm guessing that's how it works?), so instead of complete cell unwind, it merely pushes the cell growth backwards, which causes the select few to deage.
I'm also not sure whether the poison/magic/drug whatever actually deages ten years exactly because age is a finnicky thing to calculate and the two cases that had been sucessful were both a similar age, meaning that we don't know what will happen if an older/younger person ingests 4869, but in short, it definitely causes deaging.
What do you guys think? (●'◡'●)