The last requirement of my series on Generational Campaigns (see parts I, II, and II) is a method of dealing with character aging and natural life spans.
The first is rather obvious: a person's abilities change over their life. A old boxer may have great skill, but he's not as fast nor as strong as he once was. Ideally a Generational Campaign should reflect this. Simple stat modifiers are the easiest and perhaps the most effective solution, and that argues for a system that has defined Stats and Skills- so that they can be modified independently. This highlights the differing effects of age vs. experience, and details the characters with respect to each other.
Thus stat-less systems are at a disadvantage here, as are systems that simply add the total of Stat+Skill giving equal weight and range to both. There either is no place to apply the modifiers, or they come across as a flat 'level' decrease with is directly counter to the 'old but experience' feel we're going for.
There's a side benefit here as well, given that character's skill will generally increase with age (causing them to widen the difference between them and new characters), their stat will decrease. Thus it's easier to keep both in the same adventure (although the combat system in use still is the most important fact in doing this).
In addition to aging modifiers, one needs to be able to determine the natural lifespan of the character, i.e. when he'll die assuming he isn't killed as a result of an adventure. Again, one of the points of Generational Campaigns is to represent the complete lifespan of characters- and that includes when they die. It's in this way we get the final handoff to the next generation, much as we do in real life.
Unlike the previous articles in series, I've seen a number of game designs attempt this. At one point even D&D had charts for these matters. It has however dropped out of sight in more modern designs, and they never had the other needed elements in their systems to really support Generational Campaigns in any case. That last point is likely why we don't see such mechanics much today- at the end of the day they didn't serve any purpose in those games.
Previously in the comments for the first article in this series, it was mentioned that one also needed rules for marriage, sex, childbirth, etc.
I disagree.
I think that such things can be handled fine at the meta-game level ("I think Farren wants two children, but let's make it interesting and say he had a unexpected third later in life..."). Given how complex rules for things like this can quickly get, I don't think it's possible to actually manage it mechanically in a way that would cover all the bases. Besides individual characters are too small of a simple to reflect the wider setting- and thus realism or faith to the setting would hardly be damaged by such an meta-game or role-played approach.
Thus I consider details at this level to be more a matter of taste than requirement. In my own system I do have a table for family size (as well as determining the sex of one's siblings), but little more. And I tend to forgo its use for PC families leaving it up to the player's choice.