the.com/fountain of youth

means A mythical spring or fountain whose waters supposedly restore youth and reverse aging to anyone who drinks or bathes in them.

from The legend is ancient, showing up in Herodotus's writings about a spring in the land of the long-lived Ethiopians, but the phrase got cemented in popular imagination through the explorer Juan Ponce de León, who was long credited with searching for it in Florida. That part is mostly folklore — the story of his quest was written up after his death by a rival chronicler, and there's little evidence rejuvenation was his real goal. Still, the tale stuck, and 'fountain of youth' became shorthand for any promised cure-all that restores what time takes away.