I don't think it's minimizing to say that it's not clear what the sentencing considerations were in this case, or why the judge used such an odd way of speaking, and that without that information it's difficult to comment on their suitability with much confidence.
I understand that some posters think that every 13 year old boy who rapes is really just a man who should be put to death or locked up in an adult prison for life, but the law doesn't actually support that. Judges are supposed to consider things like age, the circumstances of what happened, and the mental capacity of the criminal, when sentencing.
Thirteen year olds are barely teens and in many ways function as children still, that's why grooming them sexually is so heinous. We can't have it both ways, either they don't have adult capacities in their decision making and need extra protections that adults don't, or they do. That will apply to the ones that commit crimes too.
It's possible for someone to both be guilty, but also lacking full capacity. I do't really understand why anyone would think that is the same as saying that rape (or murder, or whatever) isn't a crime.