Of course, there's a very good chance that this young man's band won't be the project that supports him into a comfortable retirement - I'd put some money on it even! However - perhaps by doing what he loves, if he ever gets to the point where he wants to make a bit more, support a family etc etc, he'll find something in a closely related field that does pay a bit more.
I don't think we should be too fast to assume that he's wasting his younger years in a dead-end pursuit. Heck, I followed my heart in an entertainment-related industry and found a way to make money from it.
Agree with those who have said he is lucky to have such a supportive and understanding father.
ER, for all intents and purposes. Part-time income <5% of annual expenditure.