The same way you would defend yourself if the allegations are made contemporaneously. In fact, it is probably easier, since the likelihood of extant forensic evidence is scant.You are older right? Without statute of limitations some women could falsely accuse you of raping them when you were a teenager, what 50 years ago? How would you defend yourself against such allegations?
After all these years, no witnesses. No crime scene to gather evidence from. It basically comes down to word vs word. I have a hard time with word vs word amounting to proof beyond a reasonable doubt.