The age of an immortal fanfic can be quite diverse. It could span centuries or just focus on a specific period within the immortal's existence. It all depends on the author's imagination and the story they want to tell.
It really varies. Some immortal fanfics start in ancient times, while others might focus on modern or future settings, so there's no fixed age.
Well, there's no standard age for an immortal fanfic. It could range from depicting the early days of an immortal's journey to exploring their experiences across different eras. It's all up to the creativity of the writer.