Idun - Goddess of Eternal Youth

Idun (whose name means "She who Renews") is the Norse Goddess of Youth and it is her magickal apples of immortality that when a Norse God or Goddess feels old age approaching, all, they have to do is to eat one of her apples in order to become young again.

Her father was a dwarf smith, Ivalde, who was considered to be one of the older families of all the Norse Gods.  Married to Bragi, the God of poetry, Idun (also spelt Idunna or Ithun) or is also considered to be the Goddess also associated with fertilityand death.  It is possible that she was originally one of the Vanir (originally a group of wild nature and fertility Gods and Goddesses who lived in Vanaheim and who were the sworn enemies of the warrior Gods of the Aesir).

In Norse myth, Idun was once abducted by the Storm Giant Thiazi and in this interval the Gods began to age rapidly.  She was eventually rescued by the trickster God, Loki, who changed her into a nut and brought her back to her hall.  Upon her return, the Gods were restored to youth.

Invocation to Idun

Idun, Asa-Goddess of long life,
Keeper of the wondrous golden apples,
Grant me the youth and long life of the Gods,
Youth and enduring life of the mind as well
as of the body.
Let my keyword be flexibility,
That my expansion in the realm of magic
May be unending. 

(source: Mistress of Enchantment)

Another wonderful invocation to Idunna is the following, accredited to Diana Pasxon

Holy fruit, in Asgard´s hearth hid,
Grows in Idunna´s girded garth:
In leafless trees life is renewed,
Silver blossoms star bare branches,
Golden the apples given to gods,
Sweet the fruit with its secret seeds.

In Midgard´s mirk, men wake from madness:
In fields a thousand years left fallow,
Sleeping seeds at last are sprouting-
Idunna, see the new day dawning,
Bear to us thy branch of blessings,
A tree of troth to bless the true.