Ali, I loved the Gap series. The characters were brilliant. It was so vast in scale too.
He said in an interview that he wrote the The Real Story: Gap into Knowledge, as a novella about a decade earlier, and left it in his desk drawer, slightly disturbed by his own writing. Then he was driving along and listening to Wagner's Ring Cycle and the story came back to him and seemed to fit: hence it became a vast and sprawling space opera
Sky, I don't really know what the reading age would be. If you were to SPOC test it, it would likely come out at Level 2-3, which means well into the adult field. Level 1 is about age 14-15.