The gods who once ruled over what would become the Sea of Stars would reward their most faithful with beautiful bottles filled with the essence of immortality, a drink that would wash away age and restore youth and vigor. Even then, their were highly prized and even more highly sought after.
With the fall of the gods and the sundering, the supply of such miraculous brew ceased but the demand for it did not. Wizards, alchemists and sorcerers bent their skills and powers to recreate such. However, lacking immortality themselves, they could only grant youth by taking it from another. The ethical or them used their own youth or refined it from pieces of neigh immortal creatures such as the phoenix, others stole and distilled the life force of youths to create theirs . . .
Bottled Youth
These rare drinks are stored in long necked, narrow bottles of opalescent glass ranging from white to black depending on the source of the youth contained within. The liquid within is a smoky color ranging from a pale ethereal white to an ashy dark gray, the white coming from immortal beings while the ashy grey from sacrificial victims, while those created with the magical of near immortal beasts have flecks of color from those beings. Those who drink the liquid can never describe its taste but it comes with fragmentary flashes of memories from where the youth (or magic) was taken from.
Sea of Stars RPG Design Journal 