whether adolscent employment is permissible in mining(coal) industry

Sir
Coal Mining Industry there were few cases detected that person employed in the mines in the age of 15 or 16 yrs under adolscent period. Now these employees has been superannuated from the service in the Yr 2018 and the length of service comes to more than 42 yrs. Is there any circular from GoI to the effect that no person can serve an organisation beyond 42 yrs of length of service. In the service file his DOA has been recorded as1975. The question is that whether gratuity will be prepared for 42 yrs length of service or actual service the employee rendered.
Kindly help by valuable suggestion and also provide any circular issued by GoI regarding length of service.

I have no idea about the circular if any of the Government of India referred to by the poster regarding any restriction on the maximum length of service of an employee in any or every organization.
Coming to the question of employment of adolescents in mines, there was a provision of every mine of Eastern Coal Fields Ltd and Western Coal Fields Ltd to employ persons below the age of 18 years. At that time, there was no restriction in the Mines Act,1952 to employ persons below 18 years of age. But after the commencement of the Mines (Amendment) Act,1983, Section 40(1) of the Mines Act,1952 explicitly prohibits the employment of persons below the age of 18 years in any mine.
Therefore, there is every possibility for the person mentioned in the post to have been employed in the mine when he was an adolescent since his year of appointment is admittedly 1975. Though the Payment of Gratuity Act,1972 puts a cap on the amount of gratuity receivable, it does not have any provision restricting the length of service rendered by an employee in an organization.
Hence, the gratuity must be paid to the employee for the actual years of service rendered by him subject to the ceiling of Rs.20 lakh.