Look at it from your parents' perspective - (i) they may not have ever considered you as the sort of person who might want to learn ballet (I'm damn sure nobody would have imagined me as a ballet dancer!) So perhaps it's not easy for them to adjust to the idea of you taking dance seriously.(ii) they may not see ballet as a sufficiently intellectual/academic pursuit (though I think it's fair to say that it stretches the mind as least as much as the body, if not more.)
Perhaps it might help them to understand that you really are interested in ballet if you're taking a visible interest in the subject as a whole - show them that you know a little about the history & background of ballet and so on. They may be worried as much as anything that you're jumping in to something that you're not really familiar with. (Though I'm not saying that knowing all about the background of ballet is a pre-requisite for starting to learn! But when they can see that you know more about the subject than they do, it'll be harder for them to argue that you shouldn't do it.)
And always remember - ultimately it's your life, not anyone elses.So good luck - and don't give up.
Anthony
P.S. If you haven't already found Tom's page, I reckon the best place to look for information and inspiration ishttp://www.panix.com/~twp/dance/dpage.htmIt certainly helped to persuade me to take up ballet (albeit rather late in life) and I've never looked back![/i]