No ones mentioned my timeline, though its a bit "rough". I'm sure you scanned over just a bit but whatever. Kishimoto said in an interview that Tobi and Madara know each other. We know two things.
1. Madara died shortly after awakening the Rinnegan
2. Madara was expecting Nagato to revive him
Based on these two things, we can assume that Nagato had Madara's eyes. We can also conclude that he died shortly after giving Nagato the Rinnegan.
Madara probably died before Obito was born or when he was an infant because Obito is near the same age as Nagato. So there's probably no way Tobi would know Madara if he were Obito.
This could also be a misconclusion. We do not really know right now, if Madara gave his own eyes to Nagato, or that he was the one " activating" this eyes inside of him. The Problem is, that we saw in the Manga, that Nagato activated the Rinnegan, but only hear, that Tobi said while taking Madaras ID " i was the one giving him this eyes" This does not mean, he took his own and put it in Nagatos Head. This would be kinda ridicoulos. I mean if Madara really died shortly after activating it, there wouldn't be time Left to give Nagato this eyes. I mean why did he searched for someone who can handle the Rinnegan? I mean, how would madara know that he would die, shortly before activating his own eyes? Do we have an furtune Teller over here? Dont belive, that he planned on giving Nagato his own eyes. I think Nagato really got the Rinnegan by himself, but Madara maybe was the key, possbily activating it.
And dont forget!
It cant be Izuna if Nagatos Eyes were Madaras! U Have to realize that, Madaras Eyes were once Izunas, that would mean, that Tobi would have the full control of the Rinnegan, as Madara, by changing its shape from Sharingan, to MS to Rinnegan, but its like Pains. So this should do enough, to prove that this Rinnegan, that tobi has got is not Madaras, or that Tobi is not Izuna.
So choose if u think it is Izuna, then Nagato activated the Rinnegan on his own.( Because the Rinnegan Eye that Tobi as Izuna got, would be his own)
But this would mean, that Tobi could also be Obito or some other character.
If u say the Rinnegan is Madaras, then u disaprove all canidates, Izuna as well as Obito. Well the only one Left would be Kagami, but he is just a noname Uchiha ~
( One small guess: anyone thought about Tobi beeing Izuna & Obito? There were so many theories, about him beeing madara in Obito body, why wont it make sense to make him Izuna in Obitos body? Beeing able to feel, and know Obitos Memorys, as well as his Eye Techniques. I checked Narutopedia etc, and found out that Obito and Izuna share many similarties, Bloodytype, Brithday, gave away there eye for someone precious, " died " on the battlefield.)