Should an adolescent offender be punished more leniently than an adult offender? Many theorists believe the answer to be in the affirmative. According to the diminished culpability model, adolescents are less mature than adults and, therefore, less responsible for their wrongdoings and should consequently be punished less harshly. This article concerns the first part of the model: the relation between immaturity and diminished responsibility. It is argued that this relation faces three normative challenges which do not allow for easy answers and which are still widely ignored in the comprehensive discussion of the diminished culpability model.