Many states have exceptions for people who are married, also age isn’t the only factor that is taken into account (mental ability is as well). There are a lot of little things like that in these laws, but the biggest one is if you go inter jurisdictional (or even extra territorial) and federal law becomes involved (must be under 16, 4+ year age difference).
Anyways, given that the girl Minsky allegedly slept with was 17, I’m not sure why the underage argument came into play at all given what I know about federal law, at least. But then IANAL. Anyways, all the articles I’ve read about Minsky in this affair say trafficking was involved but not specifically child trafficking, so I wonder if the fed’s case was based more around the trafficking and coercion aspects and not the ages of the girls involved
Also, another thing to consider: age of consent is often different when prostitution is involved, so guy could have legal consensual sex with a 16 year old, but not if they or someone else paid for it.