Two Des Moines men who were sentenced to life in prison without parole for murders committed when they were teenagers must stay behind bars, the Iowa Supreme Court ruled on Friday.

James Dorsey and Fernando Sandoval have been trying for decades to have their convictions and sentences overturned. This time lawyers argued that their clients should not have been tried as adults because the crimes were committed when they were 18 and 19 years old.

In Dorsey’s case, he was only five days past his 18th birthday when he killed Juanita Weaver during a home invasion in 1984. He argued that modern medical and social science shows the brain does not fully mature until age 25, the Des Moines Register reported.

State law states that youth who commit crimes before they turn 18 cannot be sentenced to life in prison without parole. But once someone turns 18, they face the full penalties prescribed by law.

Justice Christopher McDonald, who wrote both majority opinions, acknowledges that the 18th birthday might be an arbitrary place to draw a line, but said a line must be drawn somewhere. He cited many areas outside criminal law where turning 18 triggers new rights and responsibilities.

Sandoval was 19 in 2004 when he shot and killed two men during a fight outside a Des Moines bar. McDonald held that Sandoval has passed the statute of limitations to challenge his conviction.