TL;DR This mod adds randomness to how Sims and Pets die by Old Age, so that they don't die right after their age bar is full, but get random amounts of additional time. TL;DR

This is my very first mod, that is truly a 'mod' for The Sims 4.

How to install?
Copy the ts4script file to the 'My Documents\Electronic Arts\The Sims 4\Mods' directory, and enable script
mods in the Game Options.

Savegame Compatibility:
This mod doesn't stick to the saved games, and doesn't add any custom content. However, removing this mod from an already affected savegame will cause all overly aged Elders to die instantly.

What this mod does?
Adds a random element into the Death by Old Age: all Sims and Pets now get random time, so they won't always die right after their Elder age bar gets completely filled up. This time is granted in addition to the bonus time granted by life states, traits, and achievements, and is totally random.

Technical details:
Contrary to Sims 3, and the popular belief, the lifespan of Sims and Pets in Sims 4 is fixed. That is, after an Elder's age bar gets full, they'll die within 2 Sim days (100% chance). This death is so certain, that Elders with the exact same age will die exactly at the same time, simultaneously, in a 'mass death' effect, like in a mass murder scenario!
However, some life states, traits, and achievements grant bonus lifetime, thereb allowing certain Sims to live longer. This mod hacks this function, and introduces the random factor, thereby significantly reducing the chance of the 'mass death' scenario, while giving Sims and Pets a chance for a potentially longer life.

For the full documentation on how this mod works, read the DOCS tab of this mod page!