Idun (Ydun)
The goddess of eternal youth, married to Bragi, the god of poetry. Idun is the custodian of the golden apples of youth. When the gods feel old age approaching, they only have to eat of the apples to become young again. As a goddess of fertility, youth and death, it is possible that she was originally one of the Vanir.

Idun was once abducted by a giant and in this interval the gods began to age rapidly. She was eventually rescued by Loki who changed her into a nut and brought her back to her hall. The gods were restored to youth soon after.
Loki and Idun
Loki and Idun by the swedish artist John Bauer, 1911