This home is only six years old. There is not a light outside the garage door on building. Buyers home inspector seems to think its in the code to have an exterior light on wall of garage. Is this in the code? Front and rear entry into home has lighting on wall.

Ask the buyer to have their inspector quote chapter and verse of the code and you will gladly install a light. This is more of a bargaining tactic, not a code

From the 2008 Edition National Electric Code Section 210.70 (2) b:

For dwelling units, attached garages and detached garages with electrical power, at least one wall switch-controlled lighting outlet shall be installed to provide illumination on the exterior side of outdoor entrances or exits with grade level access. A vehicle door in a garage shall not be considered as an outdoor entrance or exit.