The state or quality of being ageless.

(relative to past) Having existed for so great a period of time that its longevity cannot be expressed. / (relative to future) Continuing infinitely or indefinitely.

(mythology, fiction, fantasy) A magical state of suspended animation, where-in the recipient is placed in a state of ageless, deathless, everlasting sleep. Well-known examples are Endymion (the lover of the Greek moon goddess, Selene), and the princess from Sleeping Beauty.