§ 235. Exemptions. Any employee who is receiving or is entitled to receive old-age insurance benefits under title two of the social security act, shall be exempt from this article upon filing with the chairman and his employer a statement, in such form as the chairman shall prescribe, waiving any and all benefits under this article. Thereafter such employee shall be exempt from any liability to contribute toward the cost of such benefits, and his employer shall be relieved of responsibility to provide for the payment of any benefits to such employee under this article.