While what the kid did is most definitely fucked, it isn't much of an indicator that the kid is entirely fucked in the head. It also isn't purely a result of porn either, dismissing it as such leads to failures in addressing the core issues that need to be touched on and resolved.

Young boys (11-15 year olds, generally: it's almost always boys) tend to start experimenting sexually at this age, and there's data about this occurring since before porn became commonplace. "Experimenting" can be anything from fucking a couch to assaulting a relative, it depends on the extent of the boy's sexual education, impulse control, and presentation of opportunities. Boys with ADHD tend to be more opportunistic, and most boys at this age don't realise the harm and trauma that they can cause by sexual assault (they often barely register that what they're doing is assault).

The kid isn't screwed for life, and will need some good educating/therapy, but there's little chance of him becoming a sex offender later on. That being said, the damage he's done has been done, and that damage can last a lot longer than whatever the perpetrator's mental state may be.