In the context of this article I see that what does it mean to be grown up means to advance to maturity I say this because in the article it says "Redemption left in their life, it's a juvenile" this means maturity because you would most likely never hear a childish person say something to straight forward like that.
I do think the juvenile offenders are being totally treated as if they were adults because juvenile people are different from adult proceedings are the terms that courts use for juvenile offenders versus adult offenders. First, juveniles commit "delinquent acts" instead of "crimes." Second, juvenile offenders have "adjudication hearings" instead of "trials."
Hope this helps~