Discuss and learn French: French vocabulary, French grammar, French culture etc.
you may say: jeune délinquant, un jeune voyou, (hooligan)
loubard/loulou is a bit old fashioned now
A few years ago a politian used the word sauvageon
You may also use "délinquant (juvénile)" or "racaille" (less polite).
"Sauvageon" is imo kind of funny, it's something you'd say to a child.