Spoilers for chapter 304 (not in order)
When a person has ofa and they also have another quirk then it causes their lifespan to be shorten and while for quirkless people are like empty glass then their suitable for the quirk that's why the other users died and All might still lived longer than the others.
Passing it to people with a quirk then they will die young plus the holders of ofa concluded that deku CANNOT pass ofa to another person anymore since he's the last holder of the quirk.
Shinomori Hikage is the 4th user of OFA and that he died at 40 which he mentioned it as an old age. He spent 18 years running away from AFO since he knew he couldn't beat him and tried to foster the power instead. But on his last years he felt the side effect of OFA on his body. he first thought that we probably was training wrongly all this time or he got some kind of disease.
But after all might's research, now it is sure that due to his death is the cause of OFA's multiple quirks and it burned his life force (which made him age faster thus died faster)
But after Shinomori, all might owned the power longer and still alive so there must be something that differentiate All might & shinomori. Then deku figured out it was because the fact All might was quirkless.
Daigoro (blackwhip user) realized that deku still does not have a mouth in the vestige world, but after the fight with Tomura deku could form vowels meaning that his mouth started to form. Shino (4th user, I gave him a nickname) explained that in the last battle with shiga, deku unexpectedly used shino's quirk. Banjo teased Shino saying he's a weirdo. The 2 looks quite friendly with each other.
The last page of the manga is Nana saying: "Back to the main topic, can you kill Shigaraki?"
