>The trouble is that I'm not convinced that anyone who hasn't evolved the inner workings of empathy by the time he is 17, ever will. I don't see it as something you wake up to discover one day. It's ingrained or it isn't.
>

This doesn't address empathy directly, but the development of the brain:

http://www.nimh.nih.gov/health/publications/teenage-brain-a-work-in-progress.shtml

Most relevant paragraph:

While this work suggests a wave of brain white matter development that flows from front to back, animal, functional brain imaging and postmortem studies have suggested that gray matter maturation flows in the opposite direction, with the frontal lobes not fully maturing until young adulthood. To confirm this in living humans, the UCLA researchers compared MRI scans of young adults, 23-30, with those of teens, 12-16.4 They looked for signs of myelin, which would imply more mature, efficient connections, within gray matter. As expected, areas of the frontal lobe showed the largest differences between young adults and teens. This increased myelination in the adult frontal cortex likely relates to the maturation of cognitive processing and other "executive" functions. Parietal and temporal areas mediating spatial, sensory, auditory and language functions appeared largely mature in the teen brain.

Tamar