Rather than 'philosopher', there is an Ancient Greek word: 'philosophos' - meaning 'lover of wisdom' (from philein ‘to love’ + sophos ‘wise’).
'Autodidact' is one possibility. Although it literally means 'self-taught', it does carry the connotations you're referring to, of self-motivation, intellectual curiosity beyond the bounds of formal schooling; enthusiasm for knowledge.
'Polymath' is another, although it refers more to depth and breadth of learning rather than the enjoyment thereof.
'Bibliophile' may be a little too specific, referring to the love of the actual artefacts of books, rather than necessarily their contents ...
... and 'bookworm' doesn't quite cut it, in this age where we get our information from so many other sources ...
If you are not averse to the idea of coining new words, how about 'cognophile'?
From the Latin roots: cogno, cognoscere - know, cognitio - knowledge, and the Greek: philos ...
This is a great question. I'm on the hunt now... I bet there's a German word for it, or something in Arabic or Hebrew ... 'cognitionis amor' was a Latin phrase meaning 'love of learning'.
(This probably won't help, but I once had a boyfriend who called me a 'knowledge junkie', lol.)