(1) Save as hereinafter otherwise provided, every driving licence granted after the commencement of this Part of this Act shall operate and be expressed to operate to license the person to whom it is granted -
(a) if or when such person has attained the age of sixteen years and is under the age of seventeen years, to drive a motor cycle, and
(b) if or when such person has attained the age of seventeen years and is under the age of eighteen years, to drive any kind of light motor vehicle or motor cycle, and
(c) if or when such person has attained the age of eighteen years and is under the age of twenty-one years, to drive any kind of mechanically propelled vehicle except a heavy motor vehicle or a locomotive while such vehicle or locomotive is actually carrying passengers for reward, and
(d) if or when such person has attained the age of twenty-one years, to drive any kind of mechanically propelled vehicle.
(2) Where a person holds, at the commencement of this Part of this Act, a l