Oh, hello Robin!
those that are tell me that some young people know themselves well enough to make that choice. I believe I would have been one of those.
Trouble is, sometimes those medically qualified people have got it disastrously wrong. And they've discounted or failed to conduct the follow ups that would have warned them how often they were getting it wrong. At present even the medically qualified don't reliably know which young people can make that choice.
Yes there may be a minority of kids who really know who they are, who will grow up to want transition whatever any one else says or does. And I get you're probably one of them. But most of us can be influenced to some extent about our body image and how it fits our gender identity. We might change our minds later about gender identity but then it's too late. And right now we're seeing the effects of a big change in social influences, many kids are deciding they are trans or gender fluid or in the wrong body because of self image and social influence, and not some permanent unshakable conviction like yours. And we only know for sure it's permanent if it doesn't change.
You have hindsight to tell you that you should have transitioned younger, other transitioners have hindsight to say they shouldn't have transitioned so young or at all. And now they are in a much worse situation than you are. So what should foresight do?
If we had a way to know for sure which kids would not change their minds, that would help. If we had a way to reverse a wrong decision, that would help. But we don't have those, and we don't have a time machine. The safest decision for young people is still - don't.