This game lol. I've been having a problem with the aging system in traveler. I recently spent an in-game week playing a family in Aurora Skies before returning to the main world I had set up. When I returned to my main world, three elderly sims had died

I was playing with an extremely long lifespan setting (like over 2000 days) and none of these sims were even close to reaching the end of the elder stage.

Just to test I loaded up China just now, which I first visited right when I started this save, and traveler immediately murdered every elderly person in that world lol. I haven't been playing anywhere near long enough for these sims to have reached the end of their lifespans.

I'm 99% sure that traveler just isn't paying attention to my lifespan settings, and is applying the 3% daily death chance to all elderly, even though they haven't reached the end of their lives yet.

Any suggestions or similar experiences? Any way to just turn the death chance off for traveler whilst keeping aging? I can kill sims off manually if need be haha.

Are the sims actually dead, or are you just getting notifications for their deaths?

I don't know how to "fix" this, exactly, but one possible workaround is to set Ageless Foreign Sims to True for each of these worlds, then manually apply extra days to the ages of all the sims in that world once you go back. That would be this command:

NRaas > MC > Sim > Intermediate > Age: Relative > [number of days to add]

If you run it from City Hall or the base camp and filter sims by Homeworld, then select All, you should get all the sims that live there, but not your visitors. Still, check the list for your own sims and deselect them if necessary.

For sims that were close to aging up, you might get an Overwatch stuck aging check or reset, followed by a forced age transition. These sims might end up a bit younger than you intended. But if you're playing on a very long lifespan, maybe it doesn't matter, and regardless, you can always fix an individual sim's age after the fact, either with Age: Relative or Age: Absolute, in the same menu.

Thank you! Yes, I've double checked and they are actually dead. They're listed under the dead for type of sim in master controller.

If I do go the manual route, is there anyway to check how many days would have been added to everyone's age by traveler? I was planning on combining my save with several other worlds and switching between them in one save file, but the maths will be a bit difficult if I'm having to figure out how many days have passed for each world individually.

I know that the aging process that takes place is EA's not SP's- and it uses the France demographics specifically. I can't see anything in that XML that specifies a lifespan, but there are a few values for killing sims when the world is considered to be overpopulated. It's possible that this function might target elders first when trying to accomplish that.
Edit: Remembered that you could actually start with switching Perform Travel Actions in Traveler settings to False to disable the pseudo-StoryProg that runs, to see if it's this that is culling the sims rather than the aging.

I could send you a version of the XML with the kill tuning set to 0, if you'd like to test if that has any effect. I'd imagine that elders that actually are in range of dying would still do so naturally.
Alternatively, for the manual method, you could hover over the game clock and note your sim-week and day each time you arrive and depart a world and add them together when you travel.

Hi. I'll test out your idea about Perform Travel Actions when I have a little free time. And yes, I would be very grateful if you could send me the tuned XML file! Or alternatively I can have a go at changing the XML file myself if I can locate the correct line. Thank you very much for your suggestions!

You may want to look at it yourself, just to see what other things get pushed by Perform Travel Actions that you might not actually want to happen.

The XML is DemographicsFrance, in the GameplayData.package.
Disabling travel actions should prevent all of the things listed in there from being pushed, but if you'd like to keep some of them you can export the file to a new package, tweak the multipliers to 0, and install it as a mod.