Marvel's Comics Asgardians were considered functionally immortal. They aged very slowly upon reaching adulthood (unlike Marvel's Olympians, who do not age AT ALL) and as such would live until killed. While the Golden Apples of Idunn are discussed in Marvel's Asgard, no mechanics for their processes are described.
The Asgardians in their most famous guises over the decades.
The difference between functional immortality and actually immortality would mean nothing to us, if their span of years numbered in the thousands. Since the myths of Norse mythology have included beings such as Odin since the 11th century, Odin would be at least 1,000 years old. He is likely much older.
This image denotes Marvel's official position on the Asgardians as aliens.
From Thor #493 (written by Warren Ellis and Mike Deodato)
Things to be remembered about Marvel's Asgardians:
- Marvel's Asgardians were based on the deities of Norse myths of old. But they are not those deities.
- They are an advanced species of humanoids who resemble humans and have technologies so advanced they appear as magic to humans.
- They are extremely long-lived as a species and have superhuman levels of strength, vigor and physical vitality. As such, myths may not take into account the actual capabilities of these beings.
- While they consume the Golden Apples of Idunn, the actual mechanics of how those Apples work have not been defined in the comics, only expressed in myths and legends.
- Most Asgardians expected to survive until Ragnarok, with the occasional death of lesser gods at the hands of their powerful enemies such as the Frost Giants or Fire Giants.