How could Moridin see for him? That would only work if Moridin was sitting on his shoulder. And people's HAIR goes gray with old age, not their eyes. The "old eyes" thing was just another expression meaning his facial expressions and so forth were those of a man who has been through a great deal of suffering and stress that normally takes a lifetime to accumulate. Moiraine was initially described in a similar way in EotW, as are other Aes Sedai in general - that is, their faces don't show the physical signs of aging, but their eyes reveal them to have too much experience for a woman as young as the skin of their faces might otherwise indicate.