About a Boy (2002)

Will Lightman (Hugh Grant) is a hip Londoner in his late thirties who one day realizes that his friends are all involved with the responsibilities of married life and that leaves him alone in the cold. Passing himself as a single father, he starts to meet a string of single mums, confident in his ability to leave them behind when they start to ask for a commitment. But Will's hope of a continued bachelorhood is interrupted when he meets 12-year old Marcus, in many ways his complete opposite.