I think your point is that there is no US standard defining what age young people can be taken advantage of. I totally agree. I just get frustrated when reading stories like this that many people (like in comments on FB in this case) seem to blame a 17-year-old for “running off” with her 27-year-old uncle when that power differential is inappropriate. (I’m not saying you feel this way.)
If she is not in touch with her family, she is missing and, as a minor, she is illegally with this much older man. I am shocked every time that people in the comments defend this type of relationship. (Again, I’m not implying you feel this way.) Jmo