Does a child suddenly become immune from harm by virtue of the age of the sexual partner, then?
Many states have a +4 rule (15 can sleep with 19, 16 with 20, 17 with 21 and then 18+ is free game). I can’t speak to the scientific attributes of whether that makes sense. Personally, I think 40 and 16 is fine, too. 200+ years ago people were married by 16.