Never really had a problem with CA drying up in the bottle unless I didn't seal it correctly.
CA should be clear in color.. When you buy a new bottle at the hobby shop, make sure it is not yellowed at all.
Typically, it should have around a year shelf life... I never buy more than a 1 or 2 oz bottle anyway.. just in case the tip goes bad.
I probably buy 3 to 4 bottles a year for my r/c car stuff... more if I'm building my other hobby stuff.