Tell him that he will have plenty of time to worry about these things. Tell him to enjoy his life and not to worry for now.

Eventually the answer will be : "If I don't pay taxes, I loose all my assets, the government will require my employer to deduct an extra amount on my pay check and if it's not enough, they will send me in jail."

The lesson is: buy bitcoin in self-custody and only buy other assets that you can afford to loose. Be smart if you want to fight the tax injustice.