Huge necro, I know, but I did a test as Marignon, using my Grand Masters, which I consume huge quantities of for research purposes. As we all know, the start with old age and die in droves.
But I placed a Healing Spring to test this out right next to my capital (map editing) and it seems Healing Spring does indeed cure afflictions aquired through Old Age.
It's not universal, though. On a single turn shift, one of my Grand Masters was healed of his affliction (Diseased) whilst another one aquired yet another affliction, and a third one didn't change at all.
I don't know what the #% of being healed by the Healing Spring is, but even if it's only 10% it may be worth it to put old aged farts on it, to keep them alive longer. I know I will, whenever I find a spring, the first thing going there is defenses, a temple and a lab.
