(a) Unless the creator expressly provides to the contrary, in any instrument executed prior to September first, nineteen hundred seventy-four, the words "minor", "minority", "infant", "infancy", "majority", "adult" and words of like import shall mean or refer to a person or a class of persons under the age of twenty-one years or who shall have reached such age, according to the context, and, unless otherwise expressly provided in any instrument executed on or after September first, nineteen hundred seventy-four shall mean or refer to a person or a class of persons under the age of eighteen years or who shall have reached such age, according to the context, except that any designation of a testamentary guardian of a "minor" or an "infant" shall refer to a guardianship of a person who has not reached the age of eighteen years, regardless of the date of the instrument containing the designation.

(b) This act shall not apply to distributions made subsequent to September first, nineteen hundred seventy-four and prior to the effective date of this act.