The blending of the Human and Demons worlds actually comes off now like an early version of Limba from DmC...and yes, the Novel is still canon, it effectively precedes the DMC3 Manga's events, which are a year before DMC3 itself. which means since Dante and Vergil at 19 in DMC3, they're 18 in the manga, and between probably between 16 and 17 in the novel.