User blog comment:B214/Question and Answers 3/@comment-4547267-20140706235742/@comment-16281343-20140707000852

Ugh. This is too painful.
 * Issei's life span when not stabilized = 0 - infinite
 * possible repercussions :
 * die because of 0 life span
 * die because of too much life
 * what to do to prevent that :
 * Rias, Akeno, and Koneko do their thing to stabilize Issei's life span

Q. What is Issei's life span now? A. Cannot be calculated.