Honestly, the younger you start perusing it the better your chances of success are.
Go for it with all your heart and surround yourself with positive people. Don't listen to those who would tell you that "you can't do it," or that it's, "just a dream."
If you want it bad enough, work hard enough, and are persistent enough, then you can make it happen.
However, don't expect to become a millionaire. Although it's a possible outcome of this path it is NOT very likely.
Becoming a professional musician is not very hard to accomplish (I'm technically a "professional" musician). All it means is that you are getting paid to play your instrument.
Becoming a "rock star" on the other hand is extremely hard to accomplish.
Best of luck!