"Are You Okay with a Slightly Older Girlfriend?" centers on the relationship dynamics between a high school student, Haruto Kirishima, and a college student, Airi Mashiro. Haruto, a reserved and introverted teenager, works part-time at a café where he meets Airi, a cheerful and confident older woman. Despite their age difference, the two develop a close bond, with Airi often teasing Haruto in a playful manner. Their interactions explore themes of maturity, vulnerability, and the challenges of navigating a relationship with differing life experiences.

The narrative delves into the complexities of their connection, highlighting Haruto's insecurities about being younger and less experienced compared to Airi. Airi, on the other hand, struggles with societal expectations and the judgment that comes with dating someone significantly younger. The story progresses through their daily lives, blending moments of lighthearted humor with deeper emotional reflections. Supporting characters, such as Haruto's classmates and Airi's friends, provide additional perspectives on their relationship, adding layers to the story.

The manga balances slice-of-life elements with romantic development, focusing on the gradual growth of Haruto and Airi's relationship. It examines how they navigate misunderstandings, external pressures, and personal growth while maintaining their bond. The series emphasizes communication and mutual understanding as key components of their evolving connection, offering a nuanced portrayal of an unconventional romance.