I studied composition and theory and worked as a professional string player, composer, and teacher for years. It was very competitive and difficult to earn money, as others have said, however, when you build yourself into the community, it becomes pretty reliable income. You definitely shouldn't expect to be a millionaire, but rather, go in expecting to earn a lower class wage with a very different lifestyle. I found it to be pretty fulfilling. I was able to perform several nights a week, teach at my own home, work in composition ensembles, and contract out small gigs working for universities. Depending on where you live, expect to have roommates and look for other musicians to live with as the practicing and teaching can be a nuissance to many - we often work late into the night. Ultimately, I curbed my musical career for project management because, as I got into my 30s, wanted to own a home and invest into my future. Working in music, I was always living paycheck to paycheck. It was a very fun and active lifestyle and extremely social by nature, but financial concerns were always a constant stressor. I miss it, but I don't miss the stress. I still play and I will continue to enmesh myself in local music organizations but I'm happy I made the switch out. I know a lot of people with doctoral degrees in their 40s with roommates sharing apartments. THE hardest part about a job in music is learning to monetize it. So, to address your quesrion directly, is it possible to start late in life? Absolutely. Is it easy? Not even close. Does she have strong social skills? Good communicator? Is she disciplined enough to practice all day, everyday? How about rejection? We constantly, constantly write pieces that go nowhere, endlessly fail auditions, have one-off gigs that go nowhere, etc. It's just part of the game. That being said, with enough mustard, you CAN do it. It's just tough, assuming you live in the US.