Do people on Threnody get really old or something? I can't work out the timeline of the events leading up to Shadows for Silence. She says her grandparents were among the first to reach the Forests of Hell, but also that the waystop has been safe for over a hundred years. Given Silence's age, her grandparents couldn't really have founded the waystop over a hundred years ago if life expectancy on Threnody is similar to other planets.
I'd have to look at the timeline myself. That might just be me not looking at continuity closely. I wasn't trying to imply people living very long.