The Youth Court would require extra resources to deal with more offenders if its age limit is increased, the Law Society says.
Cabinet is considering allowing teenagers up to the age of 19 to be dealt with by the Youth Court, rather than adult courts.
It is one of a number of recommendations being considered as part of the review of how children and young people are dealt with by government agencies.
Currently the Youth Court reviews cases involving children aged 16 and younger.
Law Society's criminal spokesperson Jonathan Krebs said increasing the age could help reduce crime.
"Providing that's accompanied by a significant increase in resourcing to the Youth Court then that would be a good thing, but if all it does is transfer a problem from one jurisdiction to another without providing the facilities to deal with it than that would be a problem."
Social Development Minister Anne Tolley told TV3's The Nation Cabinet was cautious about the idea, but said it was worth investigating.