So interesting for you to ask this kind of question because it is very important for one to get going. Bitcoin is not a Ponzi scheme just like some traders and investors pose it to be. It is a good move when we are ready to learn and it is one of the things that would help us to understand the market very well so that we can act on it without investing in the market blindly. Those who had been in the crypto market for long must have learnt how the crypto market works that would prevent them from make silly mistakes that could cost them to lose money anyhow in the market.
He is young and having information about this with his current status is just having $100 from his dad which is surely not enough for investment or trading because he needs to use this money for other things as well right now best thing is just check this all and try to understand with having work for the bitcoin could be really helpful for this kid because with this he can take good experience, and then he can use this all for the better future as well.
Right now having salary with bitcoin is also working, and he can work and also increase his skills for this is also not bad at all but still he wants to use this dad money then he can do some strategy with having some amount every month is also good idea because now most chances we will be having bullish trend which will give him good profit but for this all he again needs to understand all fundamentals of trading and holding bitcoin for the better result.