Sensible Sentencing Trust has launched a petition telling Parliament not to lift the maximum age for the Youth Court.
Children and young people up to and including 16-year-olds can be tried in Youth Courts, but advocates want that age raised to meet international standards.
The Trust's youth spokesperson Jess McVicar said the Youth Court was flawed, and often sent young offenders back to unstable households.
Miss McVicar said until that was fixed, the age should not be raised.
"The offenders that we've got at the moment going up to 17-year age, let's put something in place for them.
"Let's sort the age group out that we've got at the moment and if that system works then, do you know what, I would be absolutely open-minded to looking at a change. And i've already said that, but as the system is now, no."
Miss McVicar said if changes were shown to bring down the levels of recidivism, she would be open to raising the age.
She said police also needed to be resourced to help keep young people on track.