"Eikyū Shōnen Eternal Boys" centers on a group of middle-aged men who, despite their age, decide to pursue their dreams of becoming idols. The story begins with the formation of a unique idol group called "Eternal Boys," initiated by a talent agency seeking to break away from the conventional idol industry dominated by younger performers. The agency recruits six men in their 40s, each with distinct backgrounds and personal struggles, offering them a chance to reinvent themselves and challenge societal expectations.

The main characters include a former salaryman, a struggling actor, a single father, a former athlete, a musician, and a chef. Each member brings their own set of challenges and motivations to the group, reflecting the complexities of balancing personal lives with newfound ambitions. The narrative explores their journey as they navigate rigorous training, public scrutiny, and the pressures of the entertainment industry. Themes of perseverance, self-discovery, and camaraderie are central as the characters confront their insecurities and redefine their identities.

The plot unfolds through their interactions with each other, their families, and the public, highlighting the emotional and physical toll of their pursuit. The series delves into the dynamics of their relationships, both within the group and with external figures such as their manager, fans, and critics. As they progress, the Eternal Boys face setbacks and triumphs, gradually earning recognition and reshaping perceptions of what it means to be an idol. The story balances moments of humor, drama, and introspection, offering a nuanced portrayal of their collective and individual growth.