Dear Srividhya,
Neither the gratuity policy of the organization nor its date of commencement has any relevance to the payment of gratuity to its employees on the termination of employment. The moment the Payment of Gratuity Act,1972 becomes applicable to any establishment mentioned in section 1(3) of the Act and the contingency mentioned in sec.1(3-A), the employees of that establishment becomes eligible for gratuity on termination of their employment for the entire service rendered by them in the establishment including the service prior to the date of the application of the Act to the establishment. Therefore the particular employee mentioned in your post is eligible to get gratuity for the entire service rendered by him..