"You were only 19 years old, but you were an adult and this was clearly thought through offending," Judge Crayton said at today's sentencing.
"There was a very high level of victim harm in this case."
Last month Roigard was found guilty of the charges at a jury trial in Whanganui District Court and was acquitted on one other charge relating to another complainant.
The abuse of his victim lasted for about a year. He would get her alone and touch her at first, but the abuse became more serious the longer it went on.
Aaron Roigard was a father-of-two and is believed to be buried somewhere in rural South Taranaki, but his body has never been found.
David Roigard denies his involvement in the crime and will appeal his murder conviction and sentence in the Court of Appeal in July.