Worked in 2 PSU cumulative 5 years. Am I eligible for Gratuity?

I have worked for 5 months with a Naratna PSU and after that I have worked for 4 years and 7 months with Maharatna PSU. Technically both are owned by President of India since majority shareholding in both organization is with government. Am I eligible for Gratuity? Kindly help with any similar case in past or best way forward.

Thanks in Advance!!

First of all, understand that a company is different from its shareholder. So both being Government Companies or that the President of India is the shareholder isn't making any difference with regard to them being independent entities. From what it appears, the service in the second PSU is marginally short of the eligibility criteria.
PSUs have a policy of transferring gratuity from one establishment to another. You can explore with the initial PSU to get the gratuity transferred to the second company, though it looks difficult on paper.