Where under the terms of the Act of the eleventh and twelfth years of the reign of Her Majesty, chapter thirty-six, or under any Acts amending the same, it is provided that the nearest heir of entail for the time entitled to succeed to an entailed estate giving his consent in any application under the said Act or Acts, shall be of the age of twenty-five years complete, it shall be sufficient, after the passing of this Act, if such heir shall be of the age of twenty-one years complete, and the said Act and any amending Acts shall be read and construed as if for the provision therein in regard to the age of such heir the provision of this Act were inserted.