Nico observed that as he aged, Percy appeared increasingly juvenile, despite being three years his senior. This perception affected Nico's view of Percy, causing him to focus on the aspects of Percy’s character that he found irritating rather than charming.
Nico's mixed feelings about Percy stemmed from his unique sense of humor, which he oscillated between appreciating and finding bothersome. Rather than enjoying Percy’s playful nature, Nico chose to hone in on the traits that annoyed him, reflecting the complexities of their friendship.