(CNN) -- It began as horseplay, with two teenage stepbrothers chasing each other with blow guns and darts. But it soon escalated when one of the boys grabbed a knife. 

Michael Barton, Quantel Lotts' stepbrother, was stabbed to death at age 17. 

The older teen, Michael Barton, 17, was dead by the time he reached the hospital, stabbed twice.The younger boy, Quantel Lotts, 14, would eventually become one of Missouri's youngest lifers. 

Lotts was sentenced in Missouri's St. Francois County Circuit Court in 2002 to life in prison without parole for first-degree murder in his stepbrother's stabbing death. 

It made no difference that at the time of the deadly scuffle, Lotts was barely old enough to watch PG-13 movie and too young to drive, vote or buy beer. 

"They locked me up and threw away the keys," Lotts, now 23, said from prison. "They took away all hope for the future." 

His stepmother, the victim's mother, has forgiven Lotts and is working with lawyers to gain his release. 

Lotts is one of at least 73 U.S. inmates -- most of them minorities -- who were sentenced to spend the rest of their lives in prison for crimes committed when they were 13 or 14, according to the Equal Justice Initiative, a nonprofit organization in Alabama that defends indigent defendants and prisoners. 

The 73 are just a fraction of the more than 2,000 offenders serving life sentences for crimes they committed as minors under the age of 18. 

Across the country, most juvenile offenders and many adults are given a second chance. Charles Manson, convicted in seven notorious murders committed when he was 27, will be eligible for his 12th parole hearing in 2012. He's been denied parole 11 times. Even "Son of Sam" killer David Berkowitz, who confessed to killing six people in the 1970s when he was in his 20s, has had four parole hearings, though he has said he doesn't deserve parole and doesn't want it. 
How many were only 13 or 14 at the time of their crime?
73