Infirm person may agree with employer to accept less than prescribed compensation

Notwithstanding anything to the contrary in this Act contained, a person in respect of whom a medical practitioner has certified that, by reason of old age or serious physical infirmity or any previous injury he is specially liable to meet with an accident or to sustain a serious injury if employed as a workman at any work may, in entering into a contract of employment with any employer lawfully agree with the employer that the employer pays less than the amount payable under this Act in respect of the injury or death of that person; but no such agreement shall be valid and effectual, unless the amount agreed to be paid in respect of the injury or death is at least one-half the amount that would otherwise be payable as compensation under this Act. the prescribed