Lawyers for a Georgia death row inmate scheduled to die this week are asking a court to halt his execution, arguing the death penalty was inappropriate because of his youth and lack of maturity at the time of his crime.

Daniel Anthony Lucas is set to be put to death Wednesday at the state prison by injection of the barbiturate pentobarbital. He was 19 in April 1998 when he and another teen broke into a central Georgia home looking for cash or valuables to sell to buy drugs and killed a trucking company owner and his two children.

Lucas' lawyers argued in a court filing Tuesday that his death sentence is "constitutionally flawed."

The jury deciding his fate did not hear meaningful evidence about his youth and lack of maturity before sentencing him to die, his lawyers argued. Additionally, advances in science since his 1999 trial demonstrate the extent to which his brain was not adequately developed, rendering the death penalty inappropriate, they wrote.

In addition to the court filing, Lucas' lawyers also asked the Georgia State Board of Pardons and Paroles to spare his life, arguing that his childhood was plagued by drugs and violence but that he's been reformed in prison. The board, which was holding a clemency hearing for Lucas on Tuesday, is the only entity that can commute a death sentence.

Lucas, now 37, received the death sentence for the killings of Steven Moss, 37, his 11-year-old son Bryan and 15-year-old daughter Kristin, at their home near Macon.

Lucas and Brandon Rhode were ransacking the Moss home when Bryan Moss came home and saw them through a front window. The boy entered through a back door armed with a baseball bat, prosecutors have said. They say the two then wrestled Bryan to a chair and Lucas shot him in the shoulder.

Lucas then led the boy to a bedroom and shot him multiple times, prosecutors have said.

Rhode met Kristin as she got home from school and forced her to sit on a chair and shot her twice with a pistol, according to court records. Rhode then ambushed Steven Moss when he arrived home, shooting him four times with the same pistol. Lucas later shot all three victims again to make sure they were dead.

Moss' wife, Gerri Ann, discovered the bodies when she returned home from work.

Rhode, who was also convicted in the killings, was executed in September 2010.

Young adults, ages 18 to 20, are less mature and less responsible than those who are older, Lucas' lawyers argued. The prosecution's portrayal of Lucas at trial as a grown man was misleading, and his trial attorney failed to ask the jury to consider his youth or drug- and alcohol-induced impairment at the time of the crime, Lucas' lawyers wrote.

Society recognizes the limitations of the young adult brain when it denies certain privileges — the right to consume alcohol or buy a handgun, for example — to people under 21, they argue.

"These youth are not granted by law the same rights and entitlements of adults; and for purposes of punishment, they should not be treated the same as adults," the court filing says.

Lucas' lawyers also argue that the practice of imposing a death sentence on someone who was under 21 at the time of his crime is sharply declining. They quote Joshua Moore, an attorney with the Georgia Capital Defender, who said evidence that the brains of these offenders aren't fully developed has helped lawyers in his office negotiate plea deals for sentences less than death and has also resulted in prosecutors not seeking the death penalty for young adults.

Lucas would be the fifth inmate executed in Georgia this year.