Is Emma flirting or is this a younger sister teasing an older brother?

The age gap and the family relationship both can make this a little icky - though people talk about it less than Marianne and Colonel Brandon in Sense and Sensibility

Sir Edward's passionate praise of the Romantic novel is reminiscent of Marianne's dramatic speeches in Sense and Sensibility. This is slightly ironic considering that Edward's earlier rejection of the novel in favor of works that can be used to better oneself falls more under Sense than Sensibility.

A common theme across Austen novels is that women tend to be more meticulous about writing letters than men. In Mansfield Park, for instance, Mary Crawford laments the fact that her brother Henry writes very short letters, if at all. Similarly, in Sense and Sensibility there is frequent correspondence between Marianne, Eleanor, and their mother. It is relevant that Austen herself frequently wrote letters to her sister Cassandra. Here is a sample of their correspondence: http://www.bl.uk/learning/timeline/item126754.html

Links to common words/themes throughout the annotations

So this is helping me think of sensitivity as the condition of possibility for "sensibility" or sense-ability. Before a thing is available to be sensed, the sensitivity has to be open/operating.