Clownfish are protandrous sequential hermaphrodites. They live in groups containing a breeding female and male, and one or more non-breeding individuals. If the female is lost, the male becomes female, and one of the non-breeders becomes male (as also happens if the male is lost).
It's important that the sex change MtF happens only after the male has sexually matured and reproduced. I propose that we move to this model for human transsexualism.
Medical transition in immature subjects has multiple insuperable disadvantages
Puberty blockers, hormone blockers, and cross-sex hormones have serious side effects.
Treatments intended to prevent normal puberty also prevent normal maturation of non-reproductive body parts.
Preventing normal puberty makes it impossible to know whether it would have reversed or attenuated gender incongruence.
Early male transition can cause sterility with no option of fertility-sparing measures such as freezing sperm.
Early male transition can cause sexual dysfunction because it prevents normal development of engorgeable tissue: this also makes vaginoplasty more difficult, with a higher risk of sequelae affecting excretory functions.
Testosterone blockade makes boys unusually tall and testosterone makes girls unusually short.
My proposal
The NHS should redeploy its resources to adult-only medical transition and CAMHS.
Medical transition of physically immature subjects should be banned on ethical grounds.
The societal model should become one of sequential hermaphroditism, in which individuals have their family, and/or take fertility-sparing action such as freezing sperm, eggs, embryos or tissue, before moving to the next phase of life in their acquired ('opposite sex') gender.
Gender incongruent children under CAMHS should inter alia be given detailed information about what adult medical transition will entail, the risks and side effects, the limits on what can be achieved in terms of imitating the appearance of the other sex, and the steps they will be able to take to preserve fertility (not to put them off, but to make sure they are really well-prepared).
Advantages
Reduced side-effects and preservation of fertility and sexual function.
Higher rates of desistence and lower incidence of regret.
The purely medical benefits are particularly notable for females, because of the powerful effects of testosterone. This means unpleasant side effects – which will at least be deferred by a few years – but also means that transition is very effective (in terms of altering superficial appearance) even in mature individuals.
Psychological benefit: gender incongruent adolescents will feel that they are on the right pathway, that there is a plan, light at the end of the tunnel, and so forth, instead of being held in a massive queue and buffeted back and forth by political and medical arguments going on over their heads. And the ones that just want to feel special can bore everyone with their detailed life plan including sperm freezing, and maybe wear a Nemo badge.
Disadvantages
There's a big one. The very thing that enables a boy to develop normal sexual and reproductive function is also the thing that gives him a male appearance, physique, and behavioural traits. There is no way around this. It cannot be ethical to give feminising treatment to someone too immature to have any grasp of the value of what he is losing. The only option is to put more effort into cosmetic techniques such as FFS – and maybe the private sector can play a role here.
TL;DR Clownfish are amazing.