In the context provided it sounds like the client meant his son would be taking over as the steward of investvesting his money and was going to put it into BTC.

In the context provided it sounds like the client meant his son would be taking over as the steward of investvesting his money and was going to put it into BTC. This is not illegal in any way. It’s not any different than having an investment manager in the first place, other than it sounds like an objectively terrible idea. It’s pretty common to move around retirement accounts in the US, the most popular type are tied with your job and frequently move when you change employers.