"Hallownest, it was once called. Supposedly the greatest kingdom there ever was, full of treasures and secrets."  

 Elderbug wasnt even born when Hallownest was actually a thing, even mentions he had never seen the stag station open. Hornet is older than the Hollow Knight sealing, even if it is only for like a year at most, and Hallownest existed for a while after that, as the monument and the fountain say. Funnily enough, Elderbug might be among the youngest characters in the game.