In About a Boy, Nick Hornby shows the maturing and growth of two individuals who seemingly have nothing in common: Will Freeman and Marcus Brewer. Through the course of the novel, however, we see there is a common theme between them: they both need to act their age.

Will is a wealthy 36-year-old living off the royalties of his late father’s famous Christmas song. While his friends are settling down and starting families, Will is trendy and social; he feels sorry for his friends with wives and children. After a relationship with a single mother, Will realizes that single mothers make great women to pursue, and he invents a 2-year old son and heads to a support group for single parents.

It is there he meets twelve-year old Marcus and his mother Fiona. Marcus is in some ways more mature than Will, the result of his parents's divorce and his life experiences thus far. His mother suffers from depression and is suicidal, and this is an enormous burden for young Marcus. He wants desperately for Will to become part of their family, that way he has another family member to rely on in case something should happen to his mother. Marcus doesn't know how to be "normal" like the kids at school and is bullied because of his hair and clothes. His tastes resemble those of his mother's more than those of a 12-year-old.

Will and Marcus end up as friends (though Will is not eager at first), and this friendship benefits them both in unlikely ways. Will mentors Marcus on how to fit in and Marcus discovers Will’s lie, but is forgiving. From Marcus, Will gets a different perspective on how his life is playing out and sees how lonely he is. He meets and falls in love with a single mother Rachel, and eventually accepts and looks forward to a life with them. By the end of the novel, both characters have learned from one another and are ready to continue living in a more rewarding (and age-appropriate) way.