Completing the Passing of the Age quest in Hollow Knight: Silksong is a bit of a challenge, as you try to track the Mushroom Sage's locations across Pharloom using the riddle he left you. It's a little similar to the Great Taste of Pharloom quest in that it sees you running all over the map to find the fungi in different out-of-the-way spots.
You can't access this wish until you've acquired the Silk Soar ability in Act 3, specifically via The Dark Below quest. Once that's done, head to the right side of the Pale Lake in the Putrified Ducts (just across from Fleatopia), climb up the platforms, and use Silk Soar to enter the passage above where you'll find the riddle in question and be able to get started.
