They really screw up the translation. It's the old age devil (老いの悪魔) not aging devil. It makes more sense as to why the old guy was obsessed in the idea since get rid of aging wont help him but get rid of old age will. And this is the official translation too. Even basic google can do it better.
what going on here? the emperor just kill his entire family two chapter ago. the hero probably don't know but shouldn't he tries to contact his families.
This story just took a nose dive into the shit pile. Tetsu did behave a little strange, but this detective who seem be old friend goes out thinking he a criminal already. This is his friend or acquaintance who attend his family funeral. The detective meet randomly with Tetsu and assume the worst...
Genocide other people is wrong, but it worse when you genocide your own people. That what it's going to be happen to the island once they stop the rumbling. The world not going take the threat of Rumbling twice.