(1)Every person who-(a)is a qualified person at the commencement of this Act, or(b)becomes a qualified person after such commencement, shall,if he has not attained the age of thirty years at such commencement or, as the case may be, on the date on which he becomes a qualified person, be liable until he attains the age of thirty years, to be called up for national service for a period of not more than four years.
