You can make a script that checks each character when you select them, like so;
This will kick in for any character and only when they are selected and can give them whatever trait or ancillary you want. Then you can make the trait kill them when the turn ends or the next turn begins, or a random chance. A script like this will only work for player controlled factions since you have to select the character. This is the best type of script to use as it will not slow down your end turn times constantly checking each character every turn (if that is even possible for those with randomly named characters, I don't think it is). I never tried to make one that works for the AI, and I cannot think of any way to do it off the top of my head. I believe the CharacterSelected only works if the character is player owned (local). I don't mod this game much though so I am no authority on the subject. I can't even remember the last time I looked in the docu-whatevers they released which say what conditions, etc. can be used.
I think in PCP I just extended the max age to like 250 years. The campaign never last long enough for most of the humans to die of old age anyway, and Dwarves, Elves, and Orcs/Goblins (half the factions in the game, even in PCP) lived much longer or didn't die of old age. The few that should die (Theoden and a few others) are scripted to randomly die after so many turns. Not sure if that is exactly what I did, I can't remember. I might end up doing something like this idea though since it would be a very small and simple script (assuming it works
).
Edit;
monitor_event CharacterSelected CharacterIsLocal
and ! IsFactionAIControlled
and ! FactionReligion (elves)
and ! FactionReligion (dwarves)
and ! FactionReligion (orcs)
and AgentType = named character
console_command give_trait this FateOfMan 1
end_monitor
I just typed this up here so it isn't actual code.
The trait code will have to be different though, pretty sure removing hitpoints doesn't do anything on the strat map, and there is no guarantee they will die in battle with 0 either. A random chance would be better in my opinion as it will will seem more natural and less scripted. The random chance will kill anyone with an "oldage" trait after a random number of turns so you will not need to know their name.
Edit; I probably could have made the script and traits, and tested it by now instead of posting this
.