A teenager who pleaded guilty to stabbing a 14-year-old girl to death to pacify an intensely jealous girlfriend should have received a youth sentence of 10 years instead of an adult sentence of life, his lawyers say.

David Bagshaw was just four days shy of his 18th birthday when he lured Stefanie Rengel out of her Toronto home on New Year's Day 2008, stabbed her six times with a eight-inch kitchen knife and left her to die in a snowbank.

He pleaded guilty to first-degree murder and last year was sentenced to life in prison with no chance of parole for 10 years -- the maximum for a 17-year-old offender being sentenced as an adult.

Melissa Todorovic, his 15-year-old girlfriend at the time, was sentenced as an adult to life with no chance of parole for seven years -- the maximum adult sentence for someone her age.

Bagshaw is now appealing a year after his sentence, arguing the maximum youth sentence of 10 years, in addition to his 21 months spent in pretrial custody, was more appropriate.

"It is capable of both promoting his rehabilitation and reintegration into society and of holding him, a reluctant offender who was extremely immature at the time of the offence, accountable to society," his lawyer Delmar Doucette writes in a document filed with Ontario's Appeal Court.

A recently released schedule of upcoming appeals shows the court is set to hear Bagshaw's case on Dec. 15.

Superior Court Justice Ian Nordheimer erred in granting Bagshaw credit for time served, Doucette said, arguing he was not obliged to do so. If credit is granted it reduces the amount of time that can be served under a youth sentence, Doucette said, therefore leaving less time in which to become rehabilitated and necessitating an adult sentence.

In the Appeal Court document Doucette also takes issue with the wording of some of Nordheimer's sentencing decision, suggesting he misunderstood some of the facts of the case.

He also suggested Nordheimer placed an impossible burden of proof on the defence by saying neither of the two psychiatrists who examined Bagshaw would say "with certainty" that Bagshaw would engage in treatment.

"With respect, no responsible psychiatrist would be prepared to state with 'certainty' that a person would continue to engage in treatment, whether they had been non-compliant in the past or not," Doucette wrote.

Nordheimer found that Bagshaw and Todorovic had a sexual relationship "marked by mutual obsession and jealousy" that culminated in Bagshaw killing Rengel after months of pressure from Todorovic, who mistakenly saw Rengel as her rival.

Todorovic had been "hounding and manipulating" Bagshaw to kill Rengel for months, threatening to withhold sex, end the relationship, have sex with another boy that Bagshaw knew or kill herself unless he went through with it, the court heard.

Bagshaw went to Rengel's home the night of the murder and lured her outside with a phone call, pretending to be one of her male friends. She met up with him and he stabbed her, leaving her bleeding but alive on the ground.

Last year, Todorovic filed for an appeal of her first-degree murder conviction and sentence.