The most likely meaning of "exhilarated" based on the context is "excited."
The evidence from the text that best supports this answer is "Flynn would watch the birds as their wings carried them with ease. He felt exhilarated but frustrated." The word "exhilarated" suggests a feeling of excitement or euphoria, which is reinforced by the phrase "felt exhilarated." The phrase "but frustrated" also suggests that Flynn's emotions were intense, further supporting the idea that he was excited by the birds' flight.