Is it impossible for me to become a ballerina when I grow up?

Jazz and ballet are very, very, very, very, very, very, very similar. However, you have to start young. I doubt you'll ever become the star of a huge company. If you work hard, though, you might be able to get a minor part in a major group or a more prominent part in a community theatre. Sorry, but you're not going to star in Swan Lake. Keep working, though!