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 chance for a longer life. 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 very soon.

What this mod does?
Adds a random element into the Death by Old Age, os that all Sims and Pets now get a very random amount of time to live, after their Elder age bar gets full. This random bonus time is granted in addition to the original bonus time, granted by life states, traits, or achievements.
Due to the randomness, the chance of having a 'mass death' effect is also reduced.

Technical details:
Contrary to the popular belief, Death by Old Age in Sims 4 is not random. Sims and Pets have a fixed lifespan, which may be extended by certain life states, traits, and achievements. That is, by default, a Sim or Pet will certainly die almost instantly, when their Elder age bar gets filled up completely (100% chance).
This mod changes this behavior, and adds randomness to the Death by Old Age, by giving Sims and Pets random bonus time, depending on their species, and certain gamepaly factors. This bonus time is randomized, each time the game evaluates an Elder's aging.

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