Logical_Dot
There is a bit loophole here, first hokage died because of ashura chakra. He got disease, in sasuke retsuden. Naruto also got the same disease it was because of the abundant of yang chakra being used. He and 2nd hokage are not poisoned by daimyo.
To be honest, I haven't novel so I don't know, but Hashirama's death hasn't been explained. Let's say that he developed cancer cells, or died with cell divison, but he shouldn't be that old. You know, Tsunade lived till new Era. If it is due to cancer cells, you can say that in the fight against 4 Kage, eight jinchuuriki, 1,000s of ninjas, thousands of samurais, soldiers from the world, Hashirama died with increase cancer cells due to rapid regeneration. It's a theory of mine, and I am using this in this fic.