2. Prior to trial, or after the commencement of the trial but before the close of the people's case, the court, in the absence of the jury, must arraign the defendant upon such information and advise him or her that he or she may admit such allegation, deny it or remain mute. Depending upon the defendant's response, the trial of the indictment must proceed as follows:

1. (a) If the defendant admits that the alleged victim was less than fifteen years old at the time of the commission or attempted commission of the offense, that allegation shall be deemed established for all subsequent purposes, including sentencing pursuant to section 70.07 of the penal law.
2. (b) If the defendant denies such allegation or remains mute, the people may, by proof beyond a reasonable doubt, prove before the jury or, where the defendant has waived a jury trial, the court, that the alleged victim was less than fifteen years old at the time of the commission or attempted commission of the offense.
3. (c) Nothing in this subdivision shall prevent the people, in a trial before the court or a jury, from making reference to and introducing evidence of the victim's age.