Do all garage receptacles have to be GFCI protected, and 18 inches off the ground?
Yes, even the receptacle for a GDO in the ceiling is required to be GFCI protected. The exception for this was removed in the 2008 NEC. 

IMO the reasoning behind this is that folks will plug an extension cord in anywhere they can, even the ceiling. And many folks like to install those pull-down cord reels on the ceiling in the middle of the garage. The GDO receptacle is a super convenient place to plug these things in.

There is no height restriction in the electric code. This may be in the building code in your area.