I'm worried that my son only listens to one genre of music
What genre of music does your son only like?
He likes rock n roll music
There's no problem about only liking one music genre, especially for a young person.
Maybe, but I'm worried since he's not as talented as he thought he was. Maybe he should change his career.
Worrying about that at this stage in his life is meaningless. He's still searching and figuring things out for himself. Just give him the time and space he needs to do that.