The Gemara Health is referring to says that the Resho’im ‘know’ that they will die and they even joke about it, but they don’t really know about it. As others have said, it sounds scary for someone to be into death. It must be in a correct context.
Sender,
Rashi writes on the Pasuk where Yitzchok tells Eisav that he doesn’t know when he’ll die, that a person should worry about dying when within the five year range of his parents’ death. The interesting thing is that the years first stabilized at Avraham before declining further.