Board Thread:Manga/@comment-5774380-20161208022759/@comment-3568954-20161210152926

there is always a Loophole. if Ymir really made a deal with the devil then maybe Eren can make a deal with God or a god or something.

another option is that its not really a life span but that overuse of the actual shifting is what kills them. i could totally see it turning out that previous generations just didn't have the know how to change it. maybe grisha figured away to reverse the process and it simply hasn't been revealed yet.