Objectives <p>The questions of when and how society should sanction juvenile offenders are subject to ongoing political and scientific debates. In this study, we use a policy reform that lowered the minimum age of criminal responsibility from 15 to 14 years for a 20-month period to investigate whether lower age limits of prosecution and conviction in the legal system affect juvenile crime.</p> Methods <p>In a quasi-experimental design, we compare monthly crime rates for cohorts of 14-year-olds before, during, and after the temporary reform while controlling for the downward trend in youth crime. We use population-wide administrative registers (<i>N</i> = 162,959 individuals) to estimate individual-month panel data models as well as a range of robustness checks.</p> Results <p>We find no evidence that lowering the minimum age of criminal responsibility reduced the probability of committing crime among 14-year-olds. In fact, we observe an important increase in reported crimes during the reform, most evident among 14-year-olds with prior offending records. We find no reform effects on crime rates among 13-year-olds and 15-year-olds and the reported findings of no general deterrent effects are consistent across different crime types and robust to model specifications.</p> Conclusions <p>The age limits in the legal systems vary greatly across different jurisdictions and political discussions of when juvenile offenders should enter the criminal justice system are enduring. The findings from this study highlight important policy implications as the “tough-on-crime” motivated reform did not have the intended crime-reducing effects.</p>