The only explanation i can think of is that he killed himself. It has been stated that his chakra has a huge life force. Well maybe it used his own life force and in the process of all the fighting with madara shortened his own life span. Every action has an equal or opposite reaction.
Mabey in one of his fights, he used sage mode and nature overcame him?
The stripes on his face indicate he was not a master of sennin mode. The more stripes/body modifications on your body, the less good you are at controlling the natural energy. His eyes resemble jiriya's who was said to be an incomplete sennin mode.
It also makes sence...
Hashirama already has immense chakra, as is...
And to master it you need to take in an equal amount of chakra from nature... And maintain that.
So, it is probally hard to handle such rediculous chakra. You could easily overdo stuff
First response...
Just thinking about one of the last panels.... his face did the same thing as Tsunade when she used her healing powers. When she uses her healing jutsu it causes her to age greatly. Maybe the first had the same problem, he said " it couldn't Be helped" like he didn't want to use it because he knew what the side effects would be. He would loose his life or shorten it greatly.
Let me know what you think of the first response
Mabey in one of his fights, he used sage mode and nature overcame him?
The stripes on his face indicate he was not a master of sennin mode. The more stripes/body modifications on your body, the less good you are at controlling the natural energy. His eyes resemble jiriya's who was said to be an incomplete sennin mode.
It also makes sence...
Hashirama already has immense chakra, as is...
And to master it you need to take in an equal amount of chakra from nature... And maintain that.
So, it is probally hard to handle such rediculous chakra. You could easily overdo stuff

Sacrifice.
