Where an inspector is of opinion that a motor transport worker working in any motor transport undertaking without a certificate of fitness is an adolescent, the inspector may serve on the employer a notice requiring that such adolescent motor transport worker shall be examined by a certifying surgeon and such adolescent motor transport worker shall not, if the inspector so directs, be employed or permitted to work in any motor transport undertaking until he has been so examined and has been granted a certificate of fitness under section 23.