I thought madara was only stated as an immortal by itachi, because hes one of few who know hes still alive???
Kisame knows him too though.
The facts are madara and the 1st hokages fight where madara was supposedly dead was years and years and years before obito was even born, so why madara would then take obitos body makes no sense.
Also miggy has stated another point that obito would be dead for 8 years the time you see tobi/madara look like obito (grown up)
However saying that he does act like obito, but i dont think he has his body...thats just...weird...and pointless, why would madara need a new body? Not just that but kakashi is like 28? yet when madara took off his mask he looked wrinkly and old.
Unless tobi did die and used orochimarus soul transfer technique....which would be really funny actually because then orochimaru appears to have hardly any original ninjutsu hahaha.