Well, it's been a while since i read this book, but like i said in my first post: About Sempere-The Son: Considering the timeline of the events in this book, Sempere-The Son in here is actually the father of Daniel from The Shadow of the Wind. Isabella is Daniel's mother, who's face he can't remember at the beginning of the Shadow. So, David is not the same age as Isabella and her son Daniel, he's the same age as Isabella and her husband, which is the Daniel's father.
About Sempere-The Son:
Considering the timeline of the events in this book, Sempere-The Son in here is actually the father of Daniel from The Shadow of the Wind. Isabella is Daniel's mother, who's face he can't remember at the beginning of the Shadow.
So, David is not the same age as Isabella and her son Daniel, he's the same age as Isabella and her husband, which is the Daniel's father.