It is not legally consensual if the person is not of the age of consent.
You are quite correct. I was not using the term in the strictly legal sense. I’m sure we all recognize many cross-generational relationships are consensual (voluntary) on the part of the under-age person or even initiated by that person.
Doesn’t justify the actions of the “adult” in the case, who should be punished according to the law, but it is just silly to pretend every 16 year old who gets it on with a teacher is forced into it by violence or psychological pressure.