Which of these was the goddess of youth in Greek mythology?

Hebe in ancient Greek religion is the goddess of youth or the prime of life. She is the daughter of Zeus and his older sister, Hera. Hebe was the cupbearer for the gods and goddesses of Mount Olympus, serving their nectar and ambrosia until she married Heracles (Roman equivalent: Hercules); her successor was the divine hero Ganymede. Another title of hers for this reason is Ganymeda, meaning "Gladdening Princess". Hebe was worshipped as the goddess of forgiveness or mercy at Sicyon.

Hebe had influence over eternal youth and the ability to restore youth to mortals, a power that appears exclusive to her, as in Ovid's Metamorphoses, some gods lament their favoured mortals aging.

According to Philostratus the Elder, Hebe was youngest of the gods and responsible for keeping them eternally young and thus was the most revered by them. Her role of ensuring the eternal youth of the other gods is appropriate with her role of serving as cupbearer, as the word ambrosia has been linked to a possible Proto-Indo-European translation related to immortality, undying, and lifeforce. In art, she is typically seen with her father in the guise of an eagle, often offering a cup to him. This depiction is seen in classical engraved gems as well as later art. Eagles were connected with immortality and there was a folklore belief that the eagle (like the phoenix) had the ability to renew itself to a youthful state, making the association with Hebe logical.