I'm 18 years old and have been a 32A since I was 11 years old. Is this normal?

Thank you for your question, Kristen.  The simple answer is yes, 32A is a perfectly normal breast size.  It is also true that a woman's breast size is not static throughout her life.  The size of a woman's breasts can change during puberty, during pregnancy, during breast feeding, after pregnancy, during menopause, and with changes in weight.  It is also the case that the size and shape of a woman's breasts can be changed with surgery, by breast augmentation with implants, fat transfer to the breast, breast reduction, mastopexy (breast lift), and mastopexy with breast implants.  Happily, a woman's options in terms of improving breast shape, or changing breast size are many, and varied.  But it should be emphasized in your case that the indication to perform such a procedure is purely aesthetic, and the procedure purely elective. You can live many happy, joyous years of life as a 32A without any problems. Just don't be surprised if your breasts change size later in life, even without surgery.

Yes this is perfectly normal. Like most women if you are unhappy with your breast size you have surgical options to increase your breast size. Please see the below link for more information

This is definitely a common situation.  Not much more will probably happen to your breast size at this point.  You might consider breast augmentation surgery.