The laws determining the age of consent typically already specify the age and gender - so gender should not be left to interpretation.
Similarly, we can exclude the option of "consent" since this is what this law is about generally - whether the person is old enough to consent.
the location also should not play a role.
The best answer seems to be that if C. one party is a teacher or other trusted adult, the age of consent can be higher - because the younger person has to be protected from the abuse of power by that person.