I think tobi is obito now yeah all of you are saying he died blah blah but yeah read my theory and then decide.

So this is the story of how I think tobi came into existence.

So yeah tobi is dieing or he is dead and a dying madaara (from a disease) and finds a tobi and decides to save or revive him at this point I like to point out that madaara has a revival jutsu so even if he died he could still revive him with his rinnengan so anyway. So anyway he takes obito in and trains him as his own for the next few years and in 2-3 year time he is 15-16 he has had a growth spurt as naruto had and he is now roughly the size of an adult and due to puberty his voice is broken anyway after a failed attempt to capture kurma he goes back to maadara and they plan to plot a plan now at this point I would like to point out that you are saying how could obito match the fourth hokage? Well he probably went through alot of training and I would like to point out people such as sasuke are pretty strong for their age him be strong enough to beat orochimaru.
Maadara and obito decided to use nagato as a pawn in their plans making sure nagato gets rinengan.Now you gotta ask yourself how could to ninka mistake two civillians for parents? Well obito probably cast a genjutsu on them which caused them to kill nagatos parents.The pain and shock of the event unlocked nagatos rinnegan and so is the journey of nagato begins. Now at this point there are some people saying if it is tobi's rinnegan then belongs to maadara and he got his eyes from izuna therefore it is his but I dont think tobi meant it in a literal term and you saw the eye activate from with in nagato so tobi casted a genjutsu and the moment caused him to activate the rinnegan
He probably made sure somehow prehaps he used the dog as a way for nagato to meet yahiko and konan and used it to lead them to a place where they would meet a sanin before making it kill itself before it could be trained by the high level ninja jiraya seeing pitty and maybe a little genjutsu help he decides to train the orphans. Yahiko is later killed and danzo and hanzo is responsible maybe one of them was being told what to do prehaps by maadara or obito now at this point I think that prehaps obito is not the first tobi and it was maadara obito probably to the role of tobi a couple of times. anyway yahiko decides to make the akatski with the purpose of capturing the tailed beasts maadara dies and obito by surpassing his master and now becomes the new tobi. This brings us up to date to current events.

Points I would like to make.
Tobis skin on the left side of his face is extremely sagged this is caused when he was crushed by the boulder not all age if you look at other old characters you will see they dont have wrinkles like him.

His original left eye was gone the first time he appeared since when he uses his space time jutsu he only uses it in his right eye and kakashi supports this theory confirming that indeed it is obitos eye

Being a uchiha he can support the rinnengan.

He was a student of the fourth who was a master of space time jutsu he could have easily picked up some knowledge from him.

Also I got one more thing that also proves my theory.
If maadara was the first tobi and itachi knew then maybe when he said maadara was a former shadow of his self it wasnt maadara but prehaps obito who would obviously seem weaker in comparison?

Also in the recent manga obito obviously seem really pissed at kakashi for some reason he took the opportunity to chastise Kakashi and perpetrate his Eye of the Moon Plan stating that he wanted to create a world where people did not have to make excuses in front of graves. Therefore referring to the promise he made to protect rin and obito liked rin so could be deep hatred there.

Questions you may be asking

obito was crushed by a boulder there is no coming back how can he live from that?
from that.
We have seen alot of serious injuries in naruto over the years
the rasengan which is an s class jutsu naruto has used countless of times on people and they have managed to survive so its possible he could have survived a boulder
Tobi is way to young explain how he could have matched minato?
Itachi achived ms and age 12. He slaughtered the entire uchiha clan.
If he can do that at age 12 matching minato at age 14 or 15 is very possible

Also I would like to point out that nagato is around the age of 26-29 so he would be around obitos age during the current timeline of events it makes sense.