Legal Question in Criminal Law in Nevada

The answer to your hypothetical question is yes. Intent is irrelevant when comes to age in a statutory rape scenario. The only true legally relevant question is whether an adult slept with a minor.

In most jurisdictions, a mistaken belief that the minor was over the age of consent is a defense to the charge -- as long as the belief is both genuine and reasonable. If the 25-year-old knew or should have known that the girls was underage, then merely hearing her say she was older would not absolve him.

Because a mistaken belief is an affirmative defense, it is something the defendant must prove rather than something the prosecutor must disprove. That will usually involve putting the defendant on the stand, which can be very risky. You (or whoever the 25-year-old is) should have a lawyer and should discuss this defense with her in great detail.