Re: Tobi (Official Breakdown):All Tobi theories go here:-
I agree with the Izuna theory, here's what I have to say about it.
Izuna having lived for so long wouldn't be impossible, since he was only a couple of years older than Oonoki, since he also lived during the first war.
But, he obviously had died after having his eyes taken, but Madara having unlocked the rinnegan could have revived him and given him new eyes, which would explain why he constantly has his sharingan active since Kakashi who also had it implanted can't de-activate it either.
Also, about his age.. it probably took several years before Madara unlocked the rinnegan and revived him, so since he's revived he would be about 20 years younger than he would've been if he never had died, now.. look at Oonoki's age and remove about 20-ish years from that and compare it to what we have seen of Tobi's face, the age matches.