Some fertile minds at work here!
OK, there are two rationales being offered above for the admission of the victim’s fake ID and phony birth certificate: first, to the extent that they go to establishing the victim’s true age, which negates an element of the crime; second, to the extent that they have some impeachment value.
Unfortunately for those who lust after the Diana Degarmos of the world, neither one holds water.
As GFactor points out, if the documents are offered to prove that the victim is in fact over the age of consent, then they are out-of-court statements offered in evidence to prove the truth of the matter asserted in the statements. That is the classic definition of hearsay. Admission of any document, hearsay or otherwise, also requires foundational testimony concerning its authenticity, usually by the records custodian or other person authorized to make the certification.
So you can’t admit the phony driver’s license or birth certificate into evidence for the purpose of proving that what they say is correct, because you cannot authenticate them.
How about the second idea - impeaching the witness by showing she lied about her age?
A prior inconsistent statement is admissible as an exception to the hearsay rule, but it must have been made under oath subject to the penalty of perjury at a trial, hearing, or other proceeding, or in a deposition.
But can we just offer into evidence the fact that she lied about her age to the accused, for the inference that she’s lying now about the sex that took place? In other words, she lied about her age, so she’s more likely to be lying to the jury now.
Not likely.
As both Hamlet and chula suggest, the probative value of this is slight – especially if the girls’ testimony is cumulative to other evidence. It might be a closer question if the case is literally a “He said - she said,” affair with the only evidence of the sex act being the accusation of the victim, but in general the prejudicial value of the evidence will outweigh the probative, and it will be properly excluded.