CALGARY -- The judge who will be asked to sentence a Calgary teen for raping his four-year-old foster brother remains concerned his mental age is just six.

Youth court Judge Lynn Cook-Stanhope said despite a psychiatric assessment which says the offender is fit to be tried, she is concerned about issues raised in another report.

Both Crown and defence lawyers said the only opinion the judge should concern herself with is Dr. John Naylor's assessment of the teen.

Prosecutor Carla MacPhail and defence counsel Ian McNish said comments by another physician, Dr. Harris Yee, questioning the offenders mental capacity didn't impact Naylor's opinion.

"Dr. Yee has stated ... his calculated mental age is six, is that not an opinion?" the judge said.

"In Roman times a six-year-old was not fit," Cook-Stanhope continued.

"I don't know what I'm supposed to do and you say 'prefer one statement over the other,'" she said.

The teen, who was 13 at the time, earlier pleaded guilty to sexual assault on another boy living in the same foster home.

Court was told the offender got the idea from viewing gay porn he accessed in the residence.

McNish said based on the contents of Naylor's report, he has no concerns his client doesn't understand the legal process.

"My position is Dr. Yee was not rendering an opinion, he was rasing a question," McNish said.

He said Naylor was asked to come up with an opinion and found "the young person is fit to stand trial."

Cook-Stanhope said she hadn't viewed the contents of Naylor's report as she didn't feel it was proper for her to do so.

But she said with the permission of lawyers for both sides she will review his findings to determine if she is satisfied the psychiatrist with the Forensic Adolescent Program considered the concerns raised by Yee.

The case returns to court Oct. 10.