This is not my view. i'm not denying the science,

That's good.

You stick my brain in a little girl, my brain made age appropriate, and I'd act like a girl largely I expect...I'd definitely be treated like a girl and internalise that to how I should behave and be...i'd consider myself while always having been a man, to have been a girl.

You would be wrong. There are case studies where, because of a botched circumcision, young boys were raised as little girls, and they did not "act like a girl largely". In fact, they had a very difficult time adjusting to the social norms required of them in that gender role. Again...there's science on this. Actual human beings have been in this hypothetical circumstance. You don't have to guess. You can just literally read about what humans do in these circumstances. The parents of both young boys reported severe emotional and behavioral problems. Both children acted out repeatedly, causing both sets of parents to eventually relent and allow their children to express themselves in whatever gender role they felt comfortable. The case studies in question, both young boys eventually "transitioned" from the female persona they had been forced into, into a male presentation. On being interviewed, both young men said that they "always knew something was wrong". This is exactly what transgender people experience internally, and exactly the process of transition we go through.

as a boy so your experience was almost certainly more in line with mine than a girl's.

I find this statement unbelievably offensive, and completely inaccurate. How dare you inform me what my lived experiences are.