Hi Mable, I just read your message and I had to respond.  While it is true that most dancers start before 13, that doesn't mean that its too late for you.  It is commonly accepted that it takes 8 years to master ballet, but you can get into a good ballet sschool before then.  If you have already started taken classes I suggest that you continue to dance.  If you haven't taken class before I think that you should weigh the pros and cons of dancing.  Will you be happy if you don't dance professionally?  Do you think you can be committed to the hard work that you will have to endure to catch up to the competition?  These are just a couple questions to consider.  Whether or not you decide to do it is up to you, but you should keep in mind that you can do anything with hard work and dedication.