This is just my theory but what if when Obito was supposedly crushed when the cave completely caved in he used his space/time transporting trick to teleport what was left of his body to the other dimesion. He probably would have done this almost instincively to save his life. from there whos to say time doesnt flow differently since it is another dimension. Obito grows up much quicker and even gains a great control over his sharingan until he is able to transport himself back to the normal dimension. From here I would assume he meets zetsu somehow who helps him to fix his body. that is atleast my theory on how he would have aged so much quicker. Now as to why his personality changed so much or how he got so strong Im still not sure. However it is obvious someone else is responsible for teaching him so much history which is most likely a uchiha.