I think this should be based on the release of a studio album. Also, of course you would consider Beyoncé's career with Destiny's Child. It's part of her music career.
Anyways, Shakira released her first studio album in 1990, so she's already had a 22 year music career.
No you count from when they first released a song not cover songs from Star Search. If we followed that Usher would be about 23 yrs or more in the game because he was in a singing group when he was 11yrs old and they released an album