Problem is that people just assume obito is tobi cause the chapter was labelled obito uchiha, and cause it was one long flash back. However, Kishi could as well has done all this to tell us that it isn't Obito. He didn't paint a picture of Obito as a person who grew up bound by hatred, but by love, dreams, and beliefs.
Also as you said regarding the time of which madara died, well nagato was born 6 years before kakashi in my calculations. Here is why:
After the 3 legendary sanins fought Hanzo, the 2nd ninja war ended. Jiraya stayed to train nagato, yahiko, and konan. At this time we would be right to assume they were very young, since the 2nd war didn't last very long, and nagatos parents were killed during it.
So Nagato is at least 6 years older than Kakashi, since kakashi was born as the 3rd war started, which was also the war, where Sakumo did the mission, where he valued his comrades over the mission, and later comitted suicide. We know that this happened 5 years before kakashis gaiden.
Assuming Obito and Kakashi was born at the same year, this means nagato had the rinnengan before Obito was even born. This means Madara was dead before Obito was even born, since Madara died as he awakened the rinnengan. This means Obito and Madara had no direct contact, whatsoever. Kishi said Tobi and Madara knew eachother. Fact is Tobi cannot be Obito, even if the last chapter said so.
Now I'm not mad if it's Obito, but then Kishi shouldn't have said in an interview that tobi and madara knew eachother. Maybe he just trolled us, I have no idea, but still annoys me. Hopefully he didn't, and we will find out tobi isn't obito in his state of mind, or that 2 tobis exist, as you stated.