To start make a living as a rocker or raper? You can never be to old. If you're good enough you can find your niche, and make a decent living off of that.
To become famous, then have radio stations play your song three or four times an hour, then be on the cover of seemingly every magazine at once, then make one of the worst albums in history, then be hated by genuine music lovers? Yeah, I'd say 29 is about right.