Legislating or creating policies for 'feelings, wishes and dreams' is difficult and potentially dangerous.
Every authority/governing body needs to step back from the feelings and take a science/data view to policies.
Lots is said about high suicide rates and risk of murder amongst the trans community. This is not supported by data, there is also little in the way of good quality research about sports, prisons, crime rates etc.
So use what we know.
If a 12/13/14/15/16/17 year old walked into their GPs or a private plastic surgeon and said I want a breast enhancement as would feel more comfortable with bigger breast or labiaplasty as think I'd have better and more sex would they say yes? If a 12/13/14/15/16/17 yr old said, I'm comfortable with my gender but would like to be chemically castrated as don't like the sensation of an erection and really don't think I'll ever want to use it, would that be allowed? If a 12/13/14/15/16/17 said, I'd like puberty blockers as want to remain a child indefinitely, I've always loved Peter Pan stories, would the doctors hand over a prescription or explain why puberty is a necessary function and the risks of not having one?
If you remove the trans issue from the medical consultation and just look at the medications and surgeries, they would be red flag requests. Either outright refused or referred for counselling.
I'm not saying that at no point should a person be able to medically transition, but I am saying that the policies need to be risk averse, they need to start with a 'let's rule out other factors' starting point, just like they would for any other physical or psychiatric condition and they need to be explicit in the need to outline consequences/side effects so that fully informed consent can be obtained.