In section 188(3) of the principal Act (minimum age restrictions not to apply to the driving of vehicles of armed forces), for the words preceding " shall not apply" there shall be substituted the words " Subject to regulations made under subsection (2) of section 96 of this Act, that section (in so far as it prohibits persons under 21 from holding or obtaining a licence to drive motor vehicles or persons under 18 from holding or obtaining a licence to drive medium-sized goods vehicles) " .