To actually answer your question, if the car was taken proper care of (or close to it) than chances are your valve seals are leaking. It could also be worn piston rings, cylinder walls, or even a gasket. Unlikely though considering it isn't that old, unless it was abused.

Good idea to check the PCV valve as suggested, but I don't think it alone is what's causing that much oil use.

My '92 civic used almost that much when I switched to synthetic. After a while the seals seemed to get used to the new oil, along with a bottle of seal conditioner, and now it uses almost nothing. (cracked/broken seals won't be helped by conditioner though)