It will be no problem if he is single so he can use his money for anything he wants including gambling. But still, he needs to prepare for his future and save his money for half amount and only use the other half amount to fills his needs. He can allocate some money for gambling and be disciplined and not add more money to gambling if he loses that. He needs to stick to his rule so he can prevent more losses. But that will be different if he is already married because he needs more money for his family and if he doesn't prepare from the beginning, he may difficult to fills his family needs. So regarding how much money we are willing for gambling will depend on our finances. If we don't have much money and we don't get a big income, we don't have to try to gamble because that can get us in trouble.
Yes, you are right, in fact you make me remember when I just graduated and a company hired me, and I did that, the bad thing is that at that time I kept the money in local currency, because the country fell to the ground and I did not have it at least in USD, I had not even given it the importance of BTC what it is now, for the same work, so that fully applies to what I wanted to do that but in BTC is what I recommend the most, because not even in USD or EUR because for me fiat money is very unstable, not even gold, I would prefer gold, then people who can do it would be better in BTC to make such savings.