The district court has jurisdiction over a criminal charge that a fifteen-year-old committed sexual assault. See 4 V.S.A. 439 (district court has jurisdiction over felonies); 13 V.S.A. 3252(a) (sexual assault is a felony punishable by up to twenty years imprisonment); 33 V.S.A. 5502(a)(1)(B) (for offenses listed in 5506(a), juvenile over fourteen years of age "shall be subject to criminal proceedings as in cases commenced against adults"); 5506(a)(10) (listing sexual assault); State v. Buelow, 155 Vt. 537, 540, 587 A.2d 948, 950 (1990) (criminal court has exclusive original jurisdiction over cases involving persons between fourteen and sixteen who are charged with certain serious crimes). An improper transfer to district court may be an error if properly raised and preserved, but we do not believe it deprives the district court of jurisdiction. Thus, "a plea of guilty operates as a waiver of previous procedural shortcomings, insofar as such defects are subject to waiver." State v. Armstrong, 148 Vt. 344, 345-46, 533 A.2d 1183, 1184 (1987) (citation omitted).