It honestly doesn’t matter what the crime or the age is. The fact that we respond by spending years producing socially disabled people, and then send them back out into the world... How can this be happening. In whose interest can this possibly be?
The problem is that this makes rehabilitation more difficult which in turn leads to recidive.
Back in the 90s (when I looked into this cause it was part of political standpoints by politicians in my country) both the general public and behavioural science was on the fence whether longer punishments or shorter punishments with a focus on rehabilitation worked better. A quick search on DDG showed news articles and studies arguing both ways.
Which is why they aren't the ones who decide sentencing.