nagato was 10 year in the 2 ninja war that was the war went jiraiya get the sanin name........Some people said there's a plot hole about Madara giving Nagato his Rennigan, but I dont think there's a plot hole
During the 3rd great war, Madara was still alive and was very old as it has been show in the current manga.
Jiraya didnt meet Nagato to train him until after d war, when the 3 sennins were head home.
Someone mentioned that Jiraya had not trained the forth hokage... I for one will say ur brain and eyes are dead and need fixing by Madara or Zetsu....because if u follow the time line well, U will notice that Jiraya had already trained Minato before Minato married Kushina and before Minato became hokage. As at the 3 great war time, Minato was already a sensei (of Kakashi, Obito and Rin), thereby suggesting that he had already finished his preliminary trainings with Jiraya at a younger age (because he was considered an excellent student, who only appear once in a life time and started under Jiraya's wings from his youth, I think even before he was 12).
As for Madara giving Nagato his eyes, that happened just after d war, by then he had already rescued Obito during the war hence Obito was with him and knew about it. It was also possible to give Nagato the eyes because d war had just finished and the Uchihas were still around; so some might have died during the war and Madara just took their eyes or may be he go some Sharingan some other way :shrug:
But what bothers me is that when Itachi went to meet Madara for help to murder d Uchihas, it was actually Obito that he met up with and not Madara, therefore Obito had long hair like Madara at some point because it couldnt have been Madara himself since he was very old when he saved Obito.
obito die in the 3 ninja war