Basic criteria is completion of 5 years of service to qualify for Gratuity on resignation/retirement or discharge.
In this case the employee is not eligible.
As some body said,even if the company has a policy of benevolence, the amount so paid without eligibility will only be called an ex- gratia than Gratuity.
Where an employee having service more than six months over and above 5 years, that will have to be treated as 6 years. If it is less than six months above 5 years, the Gratuity is calculated for 5 years.