New Children's Commissioner Judge Andrew Becroft has launched a campaign to persuade Cabinet ministers to raise the upper age limit for the Youth Court from 17 to 18.
Becroft, who has just started a short two-year term as commissioner after 15 years heading the Youth Court, has written to all ministers and plans to meet with all of them to get the age raised.
The Government has already introduced a bill to implement an expert panel's proposal to raise the age limit for state care of young people in need of care and protection from 17 to 18, but ministers are believed to be divided over whether to raise the age limit for youth justice.
Helen Clark's Labour Government introduced a bill to raise the age for leaving both state care and youth justice to 18 in 2008 but the bill was dropped by John Key's incoming National Government at the end of that year.
Justice Minister Amy Adams said last year that she had asked officials to look again at the issue, but her predecessor Judith Collins - now back in Cabinet as Police and Corrections Minister - was firmly against it.