We can come to the conclusion that he really did die since he was brought back though Edo Tensei young. We know that Edo Tensei brings you back the way you were before you died. This is why Nagato still looked very weak with white hair after he revived everyone he killed in Konoha. Also Granny Chiyo was still old as well. I doubt Kabuto can bring them back at a younger age or else he would have had the ability to power Nagato up as well as fix his legs. So I am guessing the only special thing Kabuto did to Madara was allow him to be able to fully use Hashirama's powers and that was it.
There is no way to explain how he was brought back young. Also if he was planning on being revived through Nagato then we have to assume again that he going to be revived as his younger self because it wouldn't make sense for him to be revived as a very old man. I think he really did die shortly after he awoken the Rinnegan. His body died out but the only way for him to live was to be attached to the Hashirama clone plant to fuel that body with energy.
There is no way to explain how he was brought back young. Also if he was planning on being revived through Nagato then we have to assume again that he going to be revived as his younger self because it wouldn't make sense for him to be revived as a very old man. I think he really did die shortly after he awoken the Rinnegan. His body died out but the only way for him to live was to be attached to the Hashirama clone plant to fuel that body with energy.