Let me tell you you're starting down a hard road. Is music really what you want to do with your life? Are you prepared to deal with rejection and sometimes hard critisim. Can you know in your heart of hearts that you are still good even if people tell you you aren't? Still interested? Good! I'm not trying to cast a negative light on performing and persuing a career in music, but these things are a part of it, in the same way there negative aspects to any career. A career in singing has its rewards too, and these outnumber the drawbacks. Good for you that you're already thinking about your future (at 14!) Here are my suggestions, though keep in mind that I'm a classical vocalist (and currently in College) and that some of what I'll say below may or may not apply to you:
Find a good voice teacher you work well with. You'll grow so much as a vocalist, and getting the basics of good singing techniques down now are essential for success. If you're really serious about singing professionally, get as much performing experience as you can now, singing in tallent shows (like you've done before), school and community choruses, trying out for local musicals, cantoring in churches, and finally auditioning for colleges. Look for colleges with good music and vocal performance programs for the type of singing you're interested in (many schools specialize in Classical, Jazz, or Musical Theater singing, but there are some that specialize in pop, country, gospel, folk, etc...) While you're in school, start getting to know people in the business and getting your name out by finding internships and trying out for as many things as you can. After you graduate, hopefully you'll have a solid grounding in singing as well as a solid network of contacts who can get you strated. You might also want to give a recital when you graduate and advertise it well. Then your name starts getting around and getting opera roles are easy.
Professional vocal performance is a hard, but very rewarding route to persue in life. Make sure you have the drive to do it, as well as ideas for a co-career, or a "plan B" if performing is all you want to do. If you're good, you'll get the gigs, but with a few notable exceptions, it usually won't pay all the bills. I'm a Vocal Performance/ Music Education double major now, I just finished my freshman year. Education was never my "plan B" I went into school only as a music ed major, because I've wanted to be a teacher all my life. I added performance because I love to sing and perform, and it is something I could really see myself doing in conjunction with being a music teacher in a public school.
Best of Luck,
MTJF