If my son watches Lord of the Rings, and decides to take up a pipe, he can't do it until he is 21, even though a pipe is, by any scientific measure, absolutely harmless. Government says he is too immature until then to decide for himself.

What about taking Supprelin LA, with some real positives - it blocks puberty for young people who do not feel like their sex at birth - and unknown negatives? England is taking the precautionary principle about it and National Health Service has banned puberty blockers for cases of gender dysphoria or gender incongruence in minors. They're instead going to somehow conduct trials. 

Not many are impacted right now, only 100 are on the blockers at all and they will continue. The question in the US is what will President Biden do? His party is overwhelmingly inclined to be in favor of medical treatments to affirm gender and, except for vaccines starting in 2021, least likely to listen to science. His government has increasingly sought control over everything related to health, they forced non-government employees to get COVID-19 vaccines and stuffed FDA panels with epidemiologists opposed to agriculture in order to create 'evidence' for usage levels of pesticides so low they are basically a ban. 

Will they waive control in this case? The Obama administration told young people they aren't even mature enough to get off their mom's health insurance until age 26, will the Biden administration suddenly decide that young people who can't buy a gun, a cigarette or a beer can use pharmaceuticals to alter their bodies? Drug companies are all for it, of course, as are cultural mullahs, but the science picture is less clear. 

Bone damage, infertility, and mood swings in older people are acceptable informed risk but in developing bodies it is unknown. They have existed for a while, but only used for early biological puberty. The Endocrine Society says the positive effects are fully reversible but it is unknown if the negative ones will be, and kids can't give true informed consent to lots of things, which is part of why England banned it. Advocates argue that young people with gender dysphoria are more prone to anxiety, depression, and suicide and that puberty blockers will help.

It's a cultural minefield, because when government picks winners and losers in what rights young people have, only lawyers win. If the government will waive consent and call it choice in one case, it will be invalid in lots of other areas also.