Basically saying that he has given them "partial" immortality (half of the deal -- the Forsaken think they are getting the complete package but ofc they're not) since he views them a means to an end.

Consider Aginor/Balth: They were trapped outside time but not far enough from it to age. What kept them from dying?

(A counter argument would include: Well one cannot die outside time. I'd respond with: How can you age outside time? )