The ruling comes days after the United Nations urged a tougher stance on such murders.
The National newspaper cited local police commander Sergeant Simon Mek as saying it was the first sorcery-related killing in the area to reach a national court.
"So many such cases are reported but rarely go through to the high court as relatives accept their own customary ways of settlement in the village courts," Mek said.
There is a widespread belief in sorcery in PNG, where many people do not accept natural causes as an explanation for misfortune and death, and there have been a spate of recent high-profile cases.
The UN urged an end to extra-judicial killings linked to accusations of sorcery and renewed calls for the government to repeal the Sorcery Act 1971, introduced to aid the passage of witchcraft cases through the courts.
While the act criminalised the practice of sorcery, critics say that granting the phenomenon legal recognition has led to an increase in false accusations.
"The UN is deeply disturbed with the increasing reports of violence, torture and murder of persons accused of practising sorcery around the country," the UN said.
"These vigilante killings constitute murder and must not be treated with impunity."
In Aiya's case, the court heard he blamed his aunt for the death of his brother and with two accomplices, who remain at large, went to her home in 2010 and bludgeoned her on the neck and head with axes and knives.
In jailing him, Justice Mekeo Gauli said accusations of sorcery were becoming more frequent, the newspaper reported.
"In my view some are using sorcery as an excuse to terminate someone's life though the suspect may not be a sorcerer," the judge said, urging people to use the courts to settle disputes and not take the law into their own hands.