The effect you're referring to is a symptom of lack of mylenation on the neural pathways to the prefrontal cortex. It keeps developing in many people till the mid 20s.

It makes it so accessing empathy (and judgement in general) non-instantaneous for teens. Adults have the mylenation, so can far more quickly access the prefrontal cortex's gifts in a split second manner.

http://hrweb.mit.edu/worklife/youngadult/brain.html for more on this effect

While you certainly may be able to learn things as well, this is a developmental brain function issue too. There is a limited amount of training, and a certain amount of waiting, involved in getting an adult.

Thank you! Very happy to learn that for once, science backs up my mental model of something.

I believe its learned, before the age of 4 or not at all. citation? here it is:

Wikipedia article on Empathy: "most children do not show a fully fledged theory of mind until around the age of four"

Absolutely. Find anyone who tests as an introvert but behaves (in some circumstances) as an extrovert and you're looking at someone who's learned empathy as an adult.