Longevity and infertility - the silent killers.

[Ironside]

As long as there are 2 replacements, I tend to kill off every prince older than 30 or even like 26 :P Changing kings is something best done as rarely as possible!

I've never been sure about what happens when an old heir grabs the throne - I have never seen a load of mature heirs suddenly pop up, but do you at least instantly gain a lot of underage heirs that are his already existing sons? Or does noone in MTW breed until they are the king? :P

The heirs won't breed until they're married (no literal bastards here), and unless you marry a foreign princess, they won't marry until after they're kings. When the old king dies, those new immature heirs show up. They can be of the same age as the older king, so you can have 2 heirs of the same age, where one goes up first on the heir list while the other goes last (the young "uncle").

I'm fairly certain that they won't suddenly appear as mature heirs, not sure how the game keeps track on that.

[Jxrc]

The heirs won't breed until they're married (no literal bastards here), and unless you marry a foreign princess, they won't marry until after they're kings. When the old king dies, those new immature heirs show up. They can be of the same age as the older king, so you can have 2 heirs of the same age, where one goes up first on the heir list while the other goes last (the young "uncle").

100% correct

I'm fairly certain that they won't suddenly appear as mature heirs, not sure how the game keeps track on that.

They will not appear together with the new king. The game does not seem to keep track of anything on that point. I have had heirs married when 40 who became kings when 48 and had a 12 years old heir (not sure about the exact figure but pretty sure about the principle as it kind of puzzled me whne I noticed that). I kind of think that when a new married king gets crowned, there is some kind of a roll of dice and he is allocated a random number of hirs (the system is smart enough to keep a 16 years difference between father and son so that you do not end up with a 20 years old king who has an heirs aged 15).

Might be other explanation to this but that's the only one I could figure out by myself

[Vantek]

My first idea would have been that the game keeps track of the offspring of married heirs and then when the heir becomes king "forgets" about those children that would be mature, but your idea is obviously much better Jxrc, as there is no practical difference between tracking offspring of heirs and randomly generating them when needed, and randomly generating is much more convenient.