If the younger person starts a civil suit against the older person for
statutory rape, can the older person countersue for "actual" rape?
There is no civil action counterpart to statutory rape.
Is there any way that the older person can use the "actual" rape as a
defense in either a civil or criminal charge?
Statutory rape does not give the person who is defined as a victim of statutory rape to bring a civil action for money damages against the adult with whom that individual had sex. Sometimes there might be a civil action for breach of a fiduciary or confidential relationship, or intentional infliction of emotional distress/outrageous conduct. But that would be the exception, rather than the rule, and the civil action tort would not be a strict liability offense.
While statutory rape is sometimes a "strict liability crime" in the sense that actual subjective consent is not a defense, and reasonable mistake of age is not a defense, a prosecution for statutory rape still requires proof of a voluntary act by the defendant charged with the offense.
The claim that someone did not voluntarily have sex with the underaged person and instead was forced to engage in sex with the underaged person without their consent would be a valid defense to the crime. This is because it would prevent the prosecutor from proving that the defendant committed the voluntary act element of the crime beyond a reasonable doubt.
This kind of defense could also be conceptualized as the affirmative defense of duress which would still apply to this offense.
My understanding is that if the older person has been convicted
criminally for statutory rape, that would bar that person from
prevailing in a civil suit for "actual" rape. Would this be true[?]
One could bring a civil action for assault and battery in connection with a rape not implied in law by virtue of age (i.e. what you mean when you say "actual" rape).
A criminal conviction for statutory rape (for which all appeals have been exhausted) would probably be a valid defense to such a civil action pursuant to the doctrine of collateral estoppel (i.e. because a binding determination of the same issue with the same or stronger burden of proof was finally resolved on the merits in another case involving the same people). This is only true, however, because the lack of voluntary act defense would have been available in the criminal case for statutory rape.
has such a sequence of events actually happened anywhere in the United
The United States has had states with statutory rape laws for many, many decades and many hundreds of millions of people, if not billions of people, have lived in that time period. So, almost anything that could happen with respect to a widely enacted law involving activities that are possible for ordinary people to engage in has probably happened.
This said, however, I've never heard of a legal case with this fact pattern in the news media or in reported case law (although admittedly, this isn't my area of practice). The more common case which does come up from time to time is a case of brother-sister incest where there is dispute over who should be charged (usually, but not always, the older sibling, and in rare instances, both are charged).
Historically, in the overwhelming majority of cases where statutory rape charges could easily be proven, they are not brought by prosecutors.
Sometimes this is because that is what the victim wants. Historically, victims have frequently wanted this outcome, either out of hope for an ongoing relationship with the adult, or doesn't want to relive a traumatic event, or out of the well founded believe of the victim that the case would do more to harm her reputation and well being than it would to suitably punish the adult (and keep in mind that statutory rape is often a misdemeanor offense which might be punished fairly lightly at sentencing depending upon the judge).
Sometimes this is because the prosecutor sees keeping the perpetrator employed and able to pay child support when a pregnancy results as a preferable options.
Sometimes this is because proving that sexual intercourse happened with someone beyond a reasonable doubt in cases that did not result in pregnancy, when the only witnesses are the alleged defendant and the allege child victim whose credibility may be questioned, was very difficult prior to DNA evidence, widespread use of rape kits, and cheap, ubiquitous video and photography use.
Furthermore, factually, it is exceedingly uncommon for young minor girls to rape adult men, and until quite recently, the statutory rape laws applied only to female victims. Even now, with gender neutral statutory rape laws being the norm, prosecutors are much less likely prosecute an alleged statutory rape involving a male victim than a female victim.
Finally, many prosecutors feel morally justified in invoking their authority to press statutory rape charges only when they believe that there was a non-consensual sexual act committed against the victim which happened even if it was hard to prove and are reluctant to bring such charges if the prosecutor believes under the circumstances that the act was consensual in fact, even if legally the defendant is still legally guilty in those circumstances. Generally speaking, attitudes towards this have grown more harsh towards men who have sex with young minors in recent years, but historically, this was a pretty important factor.