Board Thread:Theories and Speculation/@comment-26894845-20151212061943/@comment-25122992-20151212134830

Well, it doesn't seem like the age is stimulating the Rinnegan awakening. Sasuke clearly wasn't an old man when he awakened his Rinnegan, and if we assume Hashi's cells were really given to him by Kabuto and were an actual factor of this awakening (with or without Hagoromo's powerup), the conditions are mostly the same as those of Madara: Asura's chakra possession and being on the verge of the death (some kind of emotions akin to those causing Sharingan/MS awakening). Obito had Indra's (MS) and Asura's (Hashi DNA) chakra and even was on the verge of the death as well (being struck by Kaguya's desintegration bone), but he didn't awake the Rinnegan even then. And don't tell me both eyes are required, Obito had both back then. So we can safely assume only transimmigrant is able to accomplish this.