It's a nice idea but needs to be approached carefully. Not all creatures age the same way, of course.
So a dwarf could, for example, come of age at 12, be at his peak at 100 and die at roughly 150-70. I don't know what would be ideal.
And also, what you see with athletes is that they tend to keep their raw strength into their 30s and 40s even as their agility goes.
Finally, marathon runners have a really low heart rate and usually have higher longevity. So a lot of factors play into this.
Exactly, when I talked about modders, what I had in mind were the elves of The witcher, The saga of books from Andrzej Sapkowski (read it if you really want to find an awesome magic system).
In this universe, elves are really long-lived, and they start degrading closely before death, but when they become adults, they become sterile, and so, they cannot reproduce.
This particular flaw, was the one I was thinking off when I wrote the suggestion.
You would be able to govern the statistics of health from your creatures in the raws
In the particular case of this elves, if you were to mod them in-game, apart from their different vitality from that of humans, you would add a probability of [STERILE] upon entering certain age, and with some differences in age, they would all become sterile, affecting gameplay and roleplaying
And If AI ever gets this good, a probably result from this particular effect would be that a rival civilizations end up killing all the elven children completely eliminating their ability to produce offspring
But I'm thinking out loud, what I mean Is that the way to add a versatile and satisfactory aging system would be to rawify their vitality as species, with rises, peaks and declines, and add specifical sindromes or medical conditions to happen in certain times of their life.
Thinking out loud again, this wouldn't need to be used only for showing the decadence of a species.
If you were to get creative with this system, you could make it so that a mithical creature, in the course of their lives, suffer great decline of their health, only to ''become young'' again, some years after, rejuvenating cyclically for all eternity.
You could make a race of humans that, because of an hormonal thing, would become really prone to lewdness shortly after entering the 69 year of their life.
The possibilities are endless, and would add a lot more to the game as a whole in all the mechanics, if this was made good