> I'm still completely astonished that doctors allow teenagers to undergo sex change surgery or chemical procedures before the age of sexual consent, or the right to vote.
Thankfully, there is data here.
First, sex change surgery and chemical procedures are not what you think they are. The care given to teenagers is typically "puberty blockers", which are temporary and reversible drugs that delay the onset of puberty.
These are typically given explicitly so kids can age a bit and ensure they are aren't making difficult to reverse decisions either way.
Puberty is irreversible, so temporarily delaying it gives people time to make evaluations without time pressure. You really don't want people making decisions about whether they are trans or not under the gun -- "Oh shit, if I don't make a decision now, I'm going to have puberty, so I better go go go!".
After that, kids enter the care of mental health professionals and doctors, who observe and work with that kid's community and the kid themselves for years before undergoing any semi-permanent change like hormone therapy or surgery.
These decisions are not taken lightly, and the regret rate for gender affirming care is about 1%. That regret rate is considerably smaller than regret rates for knee/hip replacements, marriage, having children, and many, many other things we widely consider to be normal healthy things to do.