And then there’s the issue that holding that objective gender exists and is innate in the same way biological sex does is a philosophical / ideological position - other positions exist. My generation (late X) were taught to see people as unique individuals differentiated by sex only for the purposes of reproductive role - that people are born ‘gendered’ is a complete anathema - society should not be in the business of assigning acceptable appearances, behaviours and attitudes to individuals based on their sex, or worse, surgically modifying people such that their apparent sex matches their gender.
(Clarification - surgery is of-course fine as the cure for untreatable gender dysphoria, and in adults as a free choice. My objection is to the belief in appropriate gender norms and appearances as being the correct ordering of individuals in society - I’d rather see a girl with masculine interests remaining comfortable with her female body, rather than asked to question her ‘gender identity’).
Many trans people that I've talked to have told me that they knew pretty early on. One school of thought says that the actual individual in question should be empowered for themselves. Another school of thought says that the parent has the right to restrict that if it goes against their beliefs.
Very tricky issue. I tend to lean towards personal autonomy. In my own way, I've been denied personal autonomy (even into my early 40s) and I tend to respect that for others. The cost of getting this wrong, regardless of which way the truth lies, can be extremely detrimental to a person's well being. My understanding is that the science points towards transition being appropriate for a person's well being.