I don't know if I have enough information to offer a response to your thoughtful question.

First, if sex is the result of coercion, it is always wrong, and incest is often coercive.

Your question leads into a discussion of "the age of consent." States establish those laws based on an arbitrary assignment of a number. The laws often don't reflect what is actually happening. Many adolescents who are under-age by the law's definition are having sex (although this has diminished somewhat in recent years.)

But laws cannot be made based on a level of maturity. Some adolescents may be capable of making responsible decisions; others are not. Some are damaged by this; others are not. But a lot of adolescents who are not strictly legal are having sex.

Another issue, that I have addressed in my writing, are the Daddy/son, Uncle/nephew role plays. Initially I struggled with this because of the implications that they were incestuous.

However, I now see this more as fetishistic (not a necessary thing but used to enhance the sexual experience.) I also see them in more of a metaphorical sense than a literal one.

For example, a young man is attracted to the characteristics frequently attributed to "daddies," (maturity, experience, safety, etc.) and not attracted to the fact there is some biologic relationship.

Here is something I wrote about it: https://medium.com/an-idea/age-as-a-factor-in-sexual-orientation-and-attraction-8a8954e87bf6

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