Adds a myristoyl group to the N-terminal glycine residue of certain cellular and viral proteins. Also able to mediate N-terminal lysine myristoylation of proteins. N-terminal glycyl-[protein] + tetradecanoyl-CoA = CoA + H(+) + N-tetradecanoylglycyl-[protein] N-terminal glycyl-L-lysyl-[protein] + tetradecanoyl-CoA = CoA + H(+) + N-terminal glycyl-(N(6)-tetradecanoyl)-L-lysyl-[protein] Belongs to the NMT family.