Iðunn, the goddess of spring and youth, was married to Bragi, the god of poetry and music. Idun was the keeper of a store of magic apples that bestowed youth on anyone who ate them.  
She would give the gods the apples to keep them young, until she was kidnapped by a giant and the gods all began to age. Once the giant was killed and Idunn released, the gods were able to regain their eternal youth.