I'm aware of the commission of a statutory rape of a 16 year old girl by a 66 year old man.

I can't speak for other states, but in California you would not be obligated to report it under the facts you state. However, do not take this as authoritative, since other facts might change this answer. If you are really concerned you should get a full consultation with a criminal defense attorney. Generally, without some professional or legal relationship with the young person, such as a counselor, teacher, parent, police officer, who are considered "mandatory reporters", you are not obligated. It is also true that many people say all kinds of untrue things on the internet just to get stimulating conversation or sympathy.