The Equality and Human Rights Commission (EHRC) has warned the Scottish government against allowing under-18s to legally change their sex.
The Scottish government wants to lower the age at which people can apply for a gender recognition certificate from the current 18 to 16.
The Gender Recognition Reform (Scotland) Bill is making its way through the Scottish Parliament and an amendment that would have kept the legal threshold at 18 has already been rejected.
In a briefing to MSPs, the EHRC raised concerns about extending the legislation to under-18s, and noted that the legal age for issues "of less significance" like driving, buying alcohol and getting a tattoo is over 16.
The equalities watchdog suggested that Holyrood approve amendments that would raise the legal threshold to 18 or otherwise "incorporate additional safeguards for 16 and 17-year-olds".
"We recognise that 16 is the age of legal capacity in Scotland, but also that higher age limits apply for several matters that are of less significance than changing legal sex, such as purchasing alcohol and tobacco, getting a tattoo or driving a car," the EHRC said.
The Scottish government's Bill proposes removing the requirement of medical evidence and reducing the period that an applicant must live in their chosen gender from two years to three months.
One amendment proposes making 16 and 17 year olds wait six months instead of three.
An October poll of 1,018 Scots by Panelbase found strong opposition to lowering the age for gender self-identification to 16, with only 19% in favour and 62% against.
The Bill already passed the first stage in the Scottish Parliament last month, despite strong opposition and the resignation of the SNP's Ash Regan as Community Safety Minister on grounds of conscience.
The Christian Institute is urging people to contact their MSPs to raise their concerns about the "terrible" legislation.
The Christian Institute's Deputy Director for Communications, Ciarán Kelly, said the Bill "further entrenches the false belief that it is possible to change sex and will cause even greater misery and confusion for children and their families".
"Children need protecting from radical gender ideology and the obvious and best thing to do is to remove 16 and 17-year-olds from the legislation completely," he said.