First,you have to keep every record of your earnings. Like bounty sheets , airdrop, other sheets.it will help you in future.
It also depends ,how much value you have.
He said it is estimated about 2 lakh INR value of coins he has and I dont really think it will cause him any trouble, even during the demonetization phase people with transfers of above 2lakh 50 thousands were asked to show there records and this being a stable phase in Indian economy I really dont thing even having assets worth 3 lakh can cause him trouble, although I would suggest him to have a PAN card issued if he is above 18 years of age.