Soo, I´m struggling to understand Traveler and aging, perhaps it´s my incompatibility with English or with understanding in general, but I don´t get the settings right:
My Sims like to travel so I have a lot of worlds they can choose from. Depending on who is traveling I have to change the hometowns sometimes, so my children and teenagers can attend school (no vacation for them!). And there are some worlds they like to travel more to and some worlds, which they haven´t visited in ages. So a few worlds haven´t been traveled to in ages by my Sims.
I tried to stop the destinations from aging by using Traveler´s anti-aging formula but this just stopped the visited world from aging when my Sims visited it, not cool.
I tried to stop them from aging by using Story Progression Caste to set non active families to not aging, but the same effect: the visited Sim don´t age during the stay, not the effect I wanted!
Because: I want the foreign worlds to stay exactly in the way I have left them!
I don´t want the foreign world to age after my Sims arrive, they are only allowed to age during my stay there!They shall only age when I play in the world!
So what am I supposed to do so that the traveling worlds stay untouched by aging, when I arrive?

When you are visiting a world and are in vacation or any kind of visitation mode (not having used Changed Hometown), no one in that world or any other can possibly age. There are no options or choices associated with this and it cannot be changed. The entire aging system is shut down in that mode, there aren't even any options in SP related to aging that should be showing during a vacation, Uni term, etc. I think Oasis Landing gets handled a bit differently, but travel to the future doesn't seem to be relevant here so we'll set that one aside.

When you are in vacation mode, it is not necessary to Change Hometowns for sims to need to go to work/school. If you want to do it this way, use Traveler > Treat as Vacation > False. That doesn't stop the vacation or invoke aging, but it does make sims go to work/school. You would want to switch that back to True before returning home or actually trying to Change Hometown.

When you are playing any world as a hometown, in other words in a regular manner, that's where Traveler > Ageless Foreign Sims comes in. That will need to be set to True for any foreign world (that is, foreign from the point of view of where you are currently playing) in which you do not want sims to age in your absence. If you travel and Change Hometown, or transition active play to a different world, Traveler > Ageless Foreign Sims needs to be checked and adjusted again as the settings will be specific to each world. SP castes and other settings have no effect on foreign worlds, only the currently being played one can possibly be simulated at any given time.

For example, suppose you are playing in Sunset Valley and have Traveler > Ageless Foreign set to True for all connected worlds or at least for Bridgeport. Sims in Bridgeport are foreign and will not age as you continue your game in Sunset Valley. Now you travel to let's say Sunlit Tides for a vacation. While in vacation mode, no one ages anywhere (including where you currently are), so the settings don't matter. But if you Change Hometown and begin playing Sunlit Tides as a homeworld, now you have to look at Traveler > Ageless Foreign again and make sure Bridgeport is set to True because Sunlit Tides won't necessary inherit the settings from Sunset Valley, where you started.

Does that help explain how this is at least supposed to work?

@igazor: a bit, to be true
at first: if I change the traveled town to be not treated as a vacation world but not to be changed into the new home world, my teenagers can´t attend school and because of this I´ve changed the hometown, so they can go to school.
And then, perhaps in a much easier English, if I change home world, then I have to adjust Traveler settings to ageless foreigns again?!? And then no-one in the left worlds ages if I return to them? (It´s my stupid day today, so have a little patience, please!) :-]

I don't know why Treat as Vacation > False is not working for your school kids. But if you are happy with doing a Change Hometown, then that works too.

Let me try to explain it this way. Mod settings are specific to the world being played, there are no global settings for an entire game of connected worlds. When playing in World A, you might have Ageless Foreign set for World B. So let's say you travel to World B and Change Hometown. World B doesn't know anything about what the settings should be for World A, you never told it to invoke Ageless. So yes, the settings in World B need to be set for World A.

Now suppose you travel to World C and invoke Change Hometown for the first time. World C doesn't yet know anything about the settings for Worlds A and B, so they need to be set there. And the next time you play World B, you need to check the settings because World C didn't exist in your game before and it won't be Ageless until you now tell it to be.

The point is, I would recommend checking on Ageless Foreign settings in every world I play around the time I begin to play it as a homeworld each time. The settings should stick within a given world, but adding more worlds to your game later will appear to undo some of that.

@igazor: thank you for your explanations! Now I get it and feel even more stupid, because it is sooo easy and I failed! :-[[
Thank you so much!!!

This is not easy and there is nothing stupid about not getting it quite right the first few times. But glad to have been of assistance.

And again, thank you!!!