N.Y. Fam. Ct. Act § 714

§ 714. Determination of age. (a) In determining the jurisdiction of\nthe court under section seven hundred thirteen the age of the respondent\nat the time the need for supervision allegedly arose is controlling.\n (b) If the respondent is within the jurisdiction of the court, but the\nproceedings were initiated after the respondent's eighteenth birthday,\nthe family court shall dismiss a petition to determine whether a person\nis in need of supervision.\n