There are a few reasons I'd like to add to the discussion of just why Andrew will not be arrested for sleeping with Ms. Guiffre (three times supposedly).
#1. First of all, the charge would have to be filed by Ms. Guiffre with the court of law in the state in which the "crime" took place. With Ms. Giuffre, I believe that would be London, New York, Palm Beach, Florida or Little St. James Island in the Virgin Islands. The only real accusation that has come to light was the incident in London. As Ms. Guiffre was of the age of consent, the Met Police found no basis to pursue the allegations issued by Ms. Guiffre further.
#2. The ongoing investigation right now into sex trafficking by Epstein and his cohorts by the FBI will not prosecute sole claims filed by the victims of Epstein such as Ms. Giuffre is. Those will have to be filed in civil court as per #1.
#3. Should charges be actually filed against Andrew in the US as to his crime of sleeping with an underage girl, then Andrew would have to be extradited to stand trial. In order for Andrew to be extradited, the crime he's accused of committing must be a crime in both the US and the UK and carry a sentence of at least a year in prison. So it stands that if Ms. Guiffre was 17 and not of the age of consent in New York or wherever she files charges, those charges are not a crime in London and extradition goes out the window. I do not know what the sentence would be for this particular crime. Remember, Epstein got 18 months in Florida but that was a "sweetheart" deal since ruled to be invalid.
What the FBI want Andrew for is to talk to him and find out from him what he knew of Epstein and Maxwell's activities over the years. This does not mean that they're looking to prosecute Andrew at all. From Andrew's actions and demeanor after all hell broke loose, it does make Andrew look like he's "hiding something" but being guilty of an actual crime is certainly not one of them at this time. Who knows what incontrovertible evidence is still to be found in all this mess?
Just my thoughts.