Board Thread:Naruto Discussions/@comment-30918569-20200829215844/@comment-36366948-20200902024156

BloodOfTheArchon wrote: "As a child, Yagura took part in the village's barbaric ritual where Academy students would be forced to kill each other in order to graduate.[2] Following the Three-Tails' revival after being "killed" in Rin Nohara, the tailed beast was sealed within a young Yagura and he learned to control its powers over the following years.[1]"

It wasn't Yagura that was the Mizukage that Zabuza attacked and it wasn't Yagura who had Sanbi when it became free and then was sealed into Rin. Yagura did tell Naruto he was an adult, meaning Yagura was at least 18 when he died. He couldn't have been 18 when he died, he had a son/daughter who then gave birth to Kagura. So it's most likely that he died in his early 20's. Also it was shown that the 3rd Mizukage looked pretty old when Hagoromo summoned his soul during the war. This probably suggests that he died of old age and they had Yagura, the Jinchuriki become Mizukage. If Yagura died only a few years before Part 1, it's safe to say that Zabuza tried to assassinate Yagura due to his barbaric reign.