I like this idea gameplay-wise (as far as mortality goes, which I don't like from the go), but it does feel way too gamey.
It's balancing between realism and gameplay. A sudden death, whilst more realistic, does not let a player bring the character to a closure and wrap things up. I am just pointing out that a sudden death without a warning is not the only option we have to near-immortality.
It has to do with what the actions of our characters matter. You do not now really risk your life and limb when entering combat. Nor do infiltrators accomplish anything on a more permanent basis. The gradual creeping of death would serve its place if it increases the thrill you feel for the actions you do with your character. Just imagine tournaments, where you might actually get hurt and lose something, but with a much lesser chance for it for the youngsters. They would feel different. Risking life and limb, as they really did back then.
Not to mention making ordinary duels count for something.
It's nothing harsh or sudden. Nothing that the players would not anticipate. It would still take quite awhile for an ordinary noble to run through his hundred hurts.
The math of it could be that the age of your character would be the percentage of the chance of losing one point when wounded. Or something similar.
