In Brazil, a young offender is a person aged between 12 and 18.
There are multiple definitions - click on the translation that matches your context.
a young person found guilty of a crime. The age of young offenders is often statutory eg in the UK a young offender is a criminal aged between 14 and 17 years, whereas in Canada the age is between 12 and 17.
Mr Clegg claims the proposals would harm efforts to rehabilitate young offenders.