Blessings: For Someone Else: Mitzva/Birchot Mitzva

You may say any blessing on a mitzva—such as kiddush, hallel, Torah—for another person, even if you have already fulfilled the mitzva for yourself, as long as that other person is required to do that mitzva.
Example Girls (12 years old and more) and women must fulfill all of the positive commandments of Shabbat including kiddush.  So even after they have already said kiddush for themselves, they may say kiddush for other Jews, including adult men.
Exception You may not say birkat ha'mazon for someone else.