Early on in Voyager ("The Phage"), Neelix lost his lungs to the Vidians, but was saved by a donation from Kes. However, since Kes' species is so short-lived...wouldn't Neelix's Ocampan lung age to the point of uselessness within a few years? Has this issue ever come up in the episodes or books?
A voice at the back of my mind told me this would have been discussed before, but I ignored it. Someone in the other thread mentioned that the Vidiians were going to be altering the lung, so I suppose they could have fixed it so it didn't age the way a normal Ocampan lung would have.