Why does the age gap between Michael and Hanna matter? (Der Vorleser)

Michael and Hanna are 15 and 36 years old, respectively, at the start of the novel. This is important, as she is old enough to be his mother, who belongs to a different generation. We are encouraged to read into this, as that they are representatives of the two generations: Hanna as the perpetrator generation, and Michael as the second generation.
Their relationship, which is definitely weird due to the age gap, can symbolise the how interconnected the two generations are, and how the second generation are implicitly involved in the process of coming to terms with Germany's past. Due to the massive age gap, we are almost forced to acknowledge and subsequently question it, which helps with this reading of the text.