On and after July 1, 1990, any person who, on June 30, 1990, was certified only as a child health associate under the laws of this state shall, upon application to the board, be granted licensure as a physician assistant. The practice of any such person shall be subject to sections 12-36-106 (5) and 12-36-107.4; except that such practice shall be limited to patients under the age of twenty-one.