I am not sure exactly what age I was when I read my first Narnia book, but I reckon I was around 8 or 9. I am still reading them. Although C S Lewis claimed that he did not intend them to be overtly Christian nor strictly allegorical, there is no doubt (as he himself admits) that there are very obvious Christian themes and spiritual insights evident in the books. Indeed, when viewing the works in retrospect, Lewis was happy to point out the parallels; even if (as he claims) he may not have set out to create them.
Reepicheep reminds us that this is not all there is and even the brave battles we fight here for truth, justice and peace, are fulfilled, bettered and completed in another place, into which we will yet enter.