Yes. If the ex-employee was eligible for gratuity at the time of leaving the services as per the Gratuity Act, then he is eligible to claim at any time, even though 5 years have elapsed now. Normally, any unpaid gratuity, if not claimed within a reasonable time, the employer is supposed to deposit it with the Commissioner under the Payment of Gratuity Act for disposal. The claim could then be forwarded to him for disposal.
In most industries, gratuity payment is now linked to the Life Insurance Corporation of India as per statutory requirements. In such cases, the claim can be forwarded for their disposal.