Teen Neighborhood Trait to elderly

Do you just want to override the trait or do you want to create a new one? (Also I didn't forget about the kotatsu animations, haven't gotten to it yet, sorry.)

To override and make it spawn elders, you'll want to edit these and switch the TEEN to ELDER where necessary.
6e0dda9f!00000000!00000000000271f5.filter_standard_walker_Teen.sim_filter.xml
0ca4c78b!00000000!0000000000006c1f.template_teen.sim_template.xml


But you might also want to edit this file for the phone affordance if you don't want elders focused on the phone.
fbc3aeeb!00000000!00000000000271f2.situation_Walkby_Ambient_Teen.situation.xml

It's a lot of files involved from what I can tell, so hopefully I covered everything. Try starting your lot trait first following LMS' tutorial. You can ignore the loot/buff section if you want since this is only for spawning elder walkbys. So the only files you need from the tutorial are the ZoneModifier and the ZoneModifierDisplayInfo.

Once you have the lot trait done, you need to clone this walkby file (same one I mentioned above with the phone affordance) and reference your new lot trait in the multiplier section.
fbc3aeeb!00000000!00000000000271f2.situation_Walkby_Ambient_Teen.situation.xml

Then clone this file and reference it in the walkby file where it says "situation_job":
9c07855f!00000000!00000000000271f3.walker_Job_Teen.situation_job.xml

Inside the situation_job file you need to clone and replace the reference for this file (one of the ones I mentioned above):
6e0dda9f!00000000!00000000000271f5.filter_standard_walker_Teen.sim_filter.xml

And then that file references this file that you need to clone as well, lol (another one from above).
0ca4c78b!00000000!0000000000006c1f.template_teen.sim_template.xml

Once you've got all of those connected, then you need to inject your walkby into each world's walkby tuning. You'll need this for injecting: brainblasted.itch.io/injection-tools
Not sure how up to date it is but just contact the creator and let him know if it's bugged.

And I think that's all you need for it. Hopefully you can get it! I recommend overriding or only injecting into one world file during your testing, before you do every single one. That way you can make sure it's working without a ton of work before hand.

Sorry for the late reply. What part are you lost on, the next step after creating the trait? First import the files I listed into your .package, then starting from the top of the list I wrote slowly give them new names and replace the references I mentioned.

So for step one you rename this file you just imported: fbc3aeeb!00000000!00000000000271f2.situation_Walkby_Ambient_Teen.situation.xml
Then inside this file is this section: 

<U n="weight_multipliers">
<L n="multipliers">
<U>
<T n="multiplier">3</T>
<L n="tests">
<L>
<V t="zone">
<U n="zone">
<U n="zone_tests">
<V n="zone_modifiers" t="enabled">
<U n="enabled">
<V n="whitelist" t="specify">
<U n="specify">
<L n="whitelist">
<T>162560<!--ZoneModifier: zoneModifiers-lotTrait_Teen_Hang_Out--></T>
</L>
</U>
</V>
</U>
</V>
</U>
</U>
</V>
</L>
</L>
</U>
</L>
</U>

Where it says 162560<!--ZoneModifier: zoneModifiers-lotTrait_Teen_Hang_Out--> you need to replace it with your new lot trait.

Then rename this file: 
9c07855f!00000000!00000000000271f3.walker_Job_Teen.situation_job.xml

And in the walby file above where you replaced the lot trait reference, you now need to replace the reference where it says 160243<!--SituationJob: walker_Job_Teen--> with your new one.
<U n="walker_job">
<T n="flavor_interaction_state">74594<!--RoleState: role_walkby_flavor_one_shot--></T>
<T n="situation_job">160243<!--SituationJob: walker_Job_Teen--></T>
<T n="walkby_state">24224<!--RoleState: rolestate_leave_now--></T>
</U>
And then just continue like that down the list. Let me know if you need me to write out more. I might have to make a tutorial for this. xD

Is this your first time creating a mod then? Would you like me to post some resources for you to look at, or just make a tutorial about it when I get the chance?