It is a
really good idea for any
professional singer, no matter what their
style, to receive professional vocal training if they value their career.
Vocal training teaches you how to breathe and use your chest muscles to support your voice and reduce the strain on your vocal cords and preserve your voice.
If your favorite aging rock star can't sing anymore, lack of training is certainly one reason for that. Whereas, a voice that sounds nearly as good as it did 20 years ago means someone was taking care of themselves.