(I also lament that this makes things really rough for the trans men for whom this is not a fad, and for whom earlier transitioning would be a huge quality of life improvement.)
Like dear cis people are you OK? Is society not transphobic enough for you? :'(
Are you worried that if a teenager is allowed to explore their gender a little that it will cause a bunch of precocious little cis girls to accidentally glance at a vial of testosterone the wrong way and grow a fantastic beard overnight?
When I started estrogen (later than I should have and fuck you Idaho) I was absolutely 100% sure that it was the right thing to try, and that I'd stop if I didn't like it. Never looked back (estrogen is tasty and I encourage everyone to try it at least once), and I had years before there was much you could call permanent.
But of course it's not the "permanent changes to bodies" that made me a 6ft tall amazonian beauty that people like Aella are concerned about. "What if we accidentally trans one of the cis??" fundamentally assumes it is OK to accidentally withhold critical medicine from countless trans people just to be "safe".