It's interesting that Madara was Edo'd in his youth; my theory is that whatever Kabuto/Orochimaru did to augment his Hashirama powers also affected Madara's age / physical state. Hashirama's power is basically raw Life Force (life itself), which is why merely his flesh can grow into a massive, body-bearing plant (directed by Madara's Will, of course).
Madara's Rinnegan, having been awakened legitimately, can revert to any level of Sharingan, or even turn its Sharingan off altogether. There's no mystery to it; if he awakened the Rinnegan, he can use it when he sees fit (is that a pun?).
EDIT: Anyone else think that only the Uchiha could get away with those haircuts, because they can see chakra through the hair anyway?
DOUBLE EDIT: My apologies to Zero, upon reading the Mangastream version (my third reading of the chapter), I finally realized it was in fact Spiral Zetsu speaking to Nagato. I edited my above post to delete the part where I doubted whether it was confirmed that Spiral Zetsu spoke.