At the end of the book ‘Inheritance’, Eragon is approximately 20 years old. Although the exact timeline of events can be a bit complex due to the differing passage of time in the story compared to our world, we can piece together his age based on key events described in the series.
When we first meet Eragon in ‘Eragon’, he is a mere 15 years old. The series spans a few years, during which Eragon undergoes significant growth and development as he trains to become a Dragon Rider, faces various challenges, and ultimately plays a critical role in the fate of Alagaësia.
By the conclusion of ‘Inheritance’, which is the fourth book in the series, Eragon has matured into a capable leader and warrior, reflecting his journey not just in age but in experience and wisdom. Therefore, by calculating the time elapsed throughout the series, we can conclude that Eragon is around 20 years old at that point.