Recent insights from neuroscientific studies on brain maturation emphasize the view that young adults are a distinct group with different needs compared to children and adults. Evidence from these studies shows that the frontal lobes of the brain continue to develop into the mid-twenties (Prior et al., 2011). It is assumed that this part of the brain deals with the regulation of impulses that may lead to criminal behaviour (see e.g., Monahan, Steinberg, Cauffman, & Mulvey, 2009; Steinberg, 2013; Strang, Chein, & Steinberg, 2013). A second compelling neuroscientific insight is that great variation between individuals exists in the rate in which this maturation occurs (Braams, van Duijvenvoorde, Peper, & Crone, 2015). These neuroscientific insights are helpful to better understand criminal behavior and how to deal with delinquent young adults in the criminal justice system. First, young (adult) offenders account for a disproportionate amount of crimes, a phenomenon that is widely known as the age-crime curve (Farrington, 1986). Second, individual variation exists in continuing criminal careers or desistance from it during young adulthood. For those who continue their criminal career and get into contact with the criminal justice system, it is seen as a challenge to motivate and engage them in any intervention as part of their sentence. Third, amongst psychosocial findings, neuroscientific insights raise the question whether immaturity can be listed as a mitigating factor in judicial decision-making. In the Netherlands, in recent decades it has been debated whether it is desirable to increase the maximum age for processing young adult offenders in a juvenile court, thereby acknowledging that they are different from adults older than 25 (Van der Laan, Beerthuizen, Barendregt, & Beijersbergen, 2016). During the political coalition in 20101 this issue was again raised and this debate eventually resulted in the introduction of the so-called ‘Adolescentenstrafrecht’ (in English referred to as ‘adolescent criminal law’) on April 1, 2014. The aforementioned neuroscientific insights regarding the immature development of the brains of young adults as well as the overrepresentation of young adults in crime rates, had resulted in the recommendation to expand and promote the application of juvenile criminal law on immature young adults. The legislative changes made in the frame of the introduction of the adolescent criminal law allowed under specific conditions for the application of juvenile criminal law for young adult offenders up to the age of 23. The main aim was creating more flexibility in the sanctioning of immature young adult offenders, thereby allowing for judicial decision-making that is tailored to the specific needs and risks of this group. Hence, immature young adults may benefit from juvenile sanctions and interventions that are available in the juvenile justice system. However, the concept of immaturity is rather elusive (Prior et al., 2011), which makes it challenging to asses which young adult is eligible for a sanction or measure from juvenile law. The aim of this paper is twofold. First, we will give a concise overview of the background of the adolescent criminal law (based on Van der Laan et al., 2016). Second, we will describe several deliberations that should be taken into account now that the concept of maturation, at least in the Netherlands, has the potential to become a primary consideration in legal decision-making.