That's likely a sign of the hens aging then, yes.
Yeah, as far as I have found on it, vitiligo is like 95% of the time just cosmetic with the occasional thing like a decline in feather quality associated with it in very few cases. Vision loss, if it were to occur in him, would occur over time and not immediately, so that's just something to look out for years down the line. Hopefully he's one that avoids that issue so that you don't have to worry about it too much! I have a friend and know of a few others who have had birds with vitiligo, though, and they have all led normal lives even after the loss of pigment associated with it.
And thanks! When bored, I tend to occupy myself by reading articles or books relating to the genetics of poultry. This just happened to be a topic that I read about not that long ago and remembered!