What this guy meant how he could have taken it if was not possible, also think he means it got crushed by the stones.
I agree that it could be Izuna and he would not be 200 years old lol. He would be around 140. He can provide himself with zetsu parts and cells to keep his body intact as we have seen. Look at when he is holding naruto for the first time with a kunai, BOTH his arms are human flesh, after the minato fight he only lost 1 arm but he has now 2 zetsu arms. I would say his body is getting more old and his other arm got weak ( that didnt get cut off ) so he replaced it.
I would say more likely that tobi is Izuna atm. WHY?
He is very wise and has been thorugh alot. His intel network is superior to others both now and historcly. AND as you mentioned when kabuto reveals Madara tobi looks get diffrent that what we have seen before its the look of sumissive can you say, for instant he saw his brother he got shocked and very mind****ed.
well thats it i think, point me out if i missed something thanks!