Answer: The young age and mental development of juvenile offenders help them work toward rehabilitation because at a younger age, juveniles are more willing to change their mindset or change their habits. When you are an adult, it is usually more difficult to change one's mindset about ways of life and things they have been doing for a long time and it can be more challenging to rehabilitate. Additionally, juveniles tend to be more willing to trust someone and build a relationship with someone who they know could help them. And that is how they can rehabilitate, by trusting and understanding the people who are there for them and can guide them through their rehabilitation. Adults may not be as open to trust people or to build relationships, which can also hinder their rehabilitation.
hope this helps :) and this is just my opinion :)