The suspect was 14 when the shooting occurred in June 2010 at their home in rural Assaria, a few miles outside Salina.
The teen was initially charged with a juvenile count of first-degree murder.
The Salina Journal reports that Saline County District Judge Patrick Thompson ruled Wednesday the suspect qualifies for trial as an adult under Kansas law.
The two boys were home alone when the shooting took place. The suspect called 911 and said the shooting was accidental, but investigators concluded otherwise.