I've always been doing the same thing... I'm a classical musician. So, my first work, when I was 15, was for the Salvation Army; they recruited brass ensembles to play next to their collection buckets during the Christmas season. They always liked to find high-school kids that could play well, because at their pay rates (minimum wage) it's hard to find good musicians.
Later on, still in high school, I kept getting hired to play with the band/orchestra at the state university next door.
I've only had one non-music job; worked in the back office of a local non-profit theater organization for two months. But it doesn't really count... they hired me to futz around in the office and do odd jobs, but it turned into me doing IT stuff and resurrecting old computers. They didn't have much for me to do sometimes, so I'd always bring my horn with me and practice in this small theater that they were using for storage... usually got in at least a full hour of practice during my 4-5 hour work day.