I started music lessons at age 6 or 7. When I was around 15, my cello teacher had to turn down a gig, and recommended me. It was in the pit orchestra for a community musical theater production, playing "Oklahoma." My mom had to drive me to my first paid gig!
While in middle school, I got recruited for the school jazz band because the teacher knew that I could read bass clef. I tried to play the school's upright basses, but they were all in horrible repair and I had no teacher, so I got an electric bass worked my way through my cello etude books over the summer.
The kids in the jazz band rhythm section formed a rock band, and we played a couple of gigs while in high school -- they were like pre-teen dances and pool parties, organized by adults.
Those gigs were all pretty much dumb luck. I wasn't serious about paid gigging until many years later, and in fact I was on the fence about whether I wanted to go with jazz, rock, or classical.