Should society intervene to prevent the risky behavior of precocious teenagers even if it would be impermissible to intervene with adults who engage in the same risky behavior? The problem is well illustrated by the legal case of the 13-year-old Dutch girl Laura Dekker, who set out in 2009 to become the youngest person ever to sail around the world alone, succeeding in January 2012. In this paper we use her case as a point of entry for discussing the fundamental question of how to demarcate childhood from adulthood. After summarizing the case, we identify a ‘demarcation dilemma’ that frames much of the public and expert debate. On the one hand, it seems morally imperative ‘to treat like alike’, which means that both children and adults should be allowed to undertake all actions for which they have the relevant competences. On the other hand, requiring proportional treatment of children and adults seems to neglect the special nature of childhood as a distinct stage in life that ends at a specific age. We introduce the notion of a ‘regime of childhood’ to deal with this problem. This regime includes several dimensions, including the limited liability for children, the supervisory responsibilities of parents, the role of age-based thresholds, and the overarching purpose of childhood as a context for developing autonomy. We argue that, all things considered, there are good reasons not to shift to a regime that offers individual children the option of qualifying for adulthood on the basis of age-neutral criteria.