In People v Jason L. (2011 NY Slip Op 03440 [4th Dept 4/29/11]) the Court rejected an attempt by a prosecutor to appeal a youthful offender adjudication holding that there is no statutory authorization for such an appeal: )

The People contend that the court abused its discretion in granting defendant youthful offender status and that, as a result, the sentence imposed is invalid as a matter of law. We conclude that the appeal must be dismissed. "CPL 450.30 (2) authorizes the People to appeal from a sentence that is invalid as a matter of law" (People v Cosme, 80 NY2d 790, 792), but that statute does not authorize the People to appeal from a youthful offender finding (see generally People v Calderon, 79 NY2d 61, 63-64, 67). Indeed, upon finding that an individual is a youthful offender, "the court must direct that the conviction be deemed vacated and replaced by a youthful offender finding[,] and the court must sentence the defendant pursuant to section 60.02 of the penal law" (CPL 720.20 [3] [emphasis added]). "[T]he youthful offender finding and the youthful offender sentence imposed thereupon constitute a youthful offender adjudication' " (Calderon, 79 NY2d at 65). Here, the People do not allege that the sentence of incarceration of 1 to 4 years is illegal. Rather, "in the guise of challenging the sentence imposed, the People are in essence attacking the validity of the defendant's underlying [youthful offender finding,] . . . [which CPL 450.30 (2)] does not permit them to do" (Cosme, 80 NY2d at 792).