''The older person is in a position of authority over the younger person. The same principle applies to work place and other sexual harassment offenses.

When you have power over someone like a priest does over their worshipers or a boss does over their employees or an adult does over a child, the relationship cannot be said to be fully consensual. They are not equals. It is very easy for the older person to manipulate the younger.''

I actually did address this under the ''Power differential'' section but I didn't address a specific case like this. Just to clarify, when I speak about ''power differentials'', I am talking about any type of imbalance between the older and younger person, whether that be physical size, intelligence, social roles, emotional equalization, etc. In the rebuttal you laid out it seems that the ''authority'' you are talking about is the type that is based on social roles, views, and norms. If it's not that type of ''authority'', it will more than likely apply any other type as well, but you can still clarify if you want.

The first issue with your argument is that ''authority'' of that form, is something that doesn't necessarily manifest as harmful or coercive physical actions or behavior since it is ultimately the views or mindset of a group of people. It obviously can if the older person decides to act in a coercive or violent manner, but that isn't a guarantee, despite what you seem to believe (at least in the first part of this rebuttal, since you say that it is ''very easy to manipulate'' later on, which implies that it isn't a guarantee).

Also, that ''Authority'' doesn't guarantee that the younger person can't consent. If you claim that it does, you are committing the non-sequitur fallacy since those two things are not logically connected. As I explained in the OP, the only requirements for consent are a desire to engage in an activity, the ability to intellectually understand the activity that you wish to engage in, and the potential consequences of that activity. Obviously, that ''authority'' has no bearing on or connection to this, unless the older person actually coerces the younger person with ACTUAL behavior or action.

There are more absurd logical implications that follow from those positions that I went over in the OP, but I'll do it again. Again, the first one comes from the fact that you seem to be assuming (again, in the first part of your rebuttal where you say that the relationship cannot be said to be fully consensual) that coercion or manipulation is GUARANTEED to occur from the older person just because the older person has that type of ''authority'' over the younger one. This is a claim that will require evidence that the older person has in fact performed a coercive behavior or action towards the younger one, otherwise, you are just making a baseless accusation and look like a paranoid schizophrenic like most people who claim this.

If you want to continue to assert that it necessarily occurs due to the presence of that type of ''authority'' again, it is ultimately a claim that has to be backed up with evidence, but it is also an argument and logic that could be used to assume that all of the interactions and supposed ''consensual'' activities between a parent and their child coercive or non-consensual since that type of ''authority'' exists in that dynamic as well (and to a greater extent).

If you want to try and say that your logic or that rule only applies to certain contexts or relationships, you will have to name a relevant and non-arbitrary difference between the parent-child context and the context that you are wishing to apply that rule to, otherwise it is a special pleading fallacy.
If you want to say it only applies to a context where sex is involved, name the characteristic or a trait of sex that is relevant to the original argument or that guarantees the manifestation of coercion from the older person.