Back to the original topic, I think the only time leniency should come in with sexual assault is if there is a significant doubt as to their full mental ability to understand the criminality of their actions. As in if you have a moderate mental disability and might have had trouble understanding the "wrongness" of their actions. Say you need an IQ of 70 to be considered to be competent to stand trial and they come in at 70-79 range. Yes they meet the minimum, but barely. And prison probably is not the best environment to send a borderline mentally disabled person. I would offer a similar caveat to mental illness, if the person barely meets the criteria for criminal responsibility. I believe that might be an appropriate reason to push for more "help" and less "time."
In this case evidence has been presented to the opposite at least in intelligence, and while his conduct might be a budding personality disorder, it appears that he understood what he was doing was wrong. So, try as adult and sentence appropriately....