In reply to Rog Wilko:
For an introduction to philosophical stuff try Stephen Law, The Philosophy Files and/or The Outer Limits.
If you want mire religious stufff, The Young Atheist's Handbook is good, actually an autobiographical book by a Bangladeshi ex-muslim about how science is better.
Or more complex science but not too much try God: The Failed Hypothesis by Victor Stenger.
John Stuart Mill was famously reading Plato in the original Greek at age 7, so for a motivated reader nothing is too much.
Post edited at 11:39