The highest court in Massachusetts ruled on Thursday that individuals under the age of 21 cannot be sentenced to life without parole, becoming the first state to do so. In a 4-3 decision overruling the previous legislative action, the court raised the minimum age from 18 to 21, citing brain development science and the Massachusetts Constitution as a source for a “contemporary standard of decency.”

The decision comes from Commonwealth v. Sheldon Mattis, a case wherein Sheldon Mattis was convicted for the shooting death of Javion Blake in 2011 when he was 18. Mattis was sentenced to life without parole and the co-defendant, who was 17 at the time, was sentenced to 15 years with the possibility of parole.

In their decision, the Massachusetts Supreme Judicial Court concluded that “emerging adults, who are 18, 19, or 20, are not fully mature.” In relying on scientific research, the court also noted that “the scientific record strongly supports the contention that emerging adults have the same core neurological characteristics as juveniles.” In concluding the decision, the court declared it unconstitutional and a violation of Article 26 of the Massachusetts Declaration of Rights as well as the Eighth Amendment of the US Constitution, which protects against cruel and unusual punishment.

The scientific record of the case presented evidence that showed that “emerging adults” lacked impulse control. Emerging adults were found to display similarities to those at the age of 16 and 17, rather than older adults. The record established that they lack a fully developed prefrontal cortex that regulates impulse.

According to the court, Massachusetts is only one of ten states that require 18 to 21-year-olds who are convicted of murder in the first degree to be sentenced to life without parole.

Individuals have advocated for change in the criminal justice system since the 2013 ruling in Mattis. The attorney who represented Mattis, Ruth Greenberg, called the court’s decision “courageous.” Greenberg said, “The Supreme Judicial Court has set the standard for the nation. We’re the first, and won’t be the last, to recognize that people under 21 are not deserving of punishment of life without the possibility of parole.”

The decision allows anyone who has been sentenced to life without parole before the newly initiated parole system introduced in July 2014 for minors convicted of first-degree murder to become eligible for parole after serving 15 years. This allows for individuals, like Mattis, to be resentenced in accordance with the decision. Anyone following the date must serve between 20 and 35 years before parole consideration.