All human adults, when they were still babies in the womb were for a period of time anatomically of ambiguous/neutral gender (with mostly female looking external genitalia). I know that because I have seen such mentioned and illustrated in college textbooks on human sexuality.
That is utterly wrong propagandistic garbage.
A child develops visually distinct male or female organs as soon as 6 weeks into pregnancy which is when the baby is the size of a grain of rice, sometimes before the women even knows she's pregnant. Just because YOU can't see it doesn't mean it isn't there, we have powerful imaging techniques these days that can definitely discriminate.
Whether they develop male or female is dependent on the chromosomes, so whether someone is male or female and a ton of other attributes is decided at the time of conception. It's not a random process that happens later in life.
Whether someone identifies as male or female though is highly dependent on their environment. Children that are abused at a young age more often develop transgender attributes.
Adolescents that became transgender are up to twice as likely to have been victims of psychological abuse (odds ratio [OR] = 1.84), physical abuse (OR = 1.61), and sexual abuse (OR = 2.04) before they became sexually aware.
The researchers found that 73, 39, and 19 percent of transgender adolescents reported psychological abuse, physical abuse, and sexual abuse, respectively. Which is insane, nearly the ENTIRE community of transgenders are child abuse survivors and the majority go without appropriate counseling for the trauma they experienced.