I meant "when they age".(oops!)
Mariah Carey's voice apparently has changed quite a bit and her voice is less clear. Elton John's voice has become lower after surgery, but his voice still has energy. Apparently, singing is very hard on the vocal chords and if a certain singing style that puts stress on the vocal chords is maintained, a singer can lose his/her voice. Akina Nakamori, famous Japanese singer can't sing like she used to. Her voice is almost half-gone, I was disappointed when I saw her on youtube.In her case, she was using drugs, so I don't think it was her singing style that did her voice in.