Hashirama died in the war not long after the founding of Konoha but not before passing the title of Hokage on to Tobirama, who also died fighting off enemies. Noble deaths.
I have no idea how anyone could beat Hashirama in battle during that time even if it was a ninja army. My guess is Natural causes for him. Tobirama died in battle, I believe the gold and silver brothers were involved in his death.
don't see how hashi died form old age
like that would not make sens for tobirama is young when he died and he was hokage at a young age so we can assume that either hashi died from over using his heal jutsu or he got killed