Remember I told you about my little cousin? I started giving him injections of estradiol undecanoate (takes over two months to clear from the body, keeping E levels stable) when he was 9. His parents started taking him to doctors, but no one could figure out why he had so much estradiol in his system. And I still visit him every couple of months and give him an injection when he's asleep. Because I wanted a sister. HRT works best when started early.
To be honest, my sister is not happy with how her puberty looks. But I hope she will accept it.