Your dentist may have said that because much of the development of the face occurs during the growth spurt at puberty. Since growth of the facial bones is completed at your age, correction of skeletal imbalances may require surgery. If you're really keen to consider braces then your dentist can refer you to an Orthodontist who will be in a better position to advise you whether getting braces is an option for you. As an adult, there are a number of subtle types of braces available should you be more self conscious about wearing the traditional metal or ceramic ones. Examples include Sapphire braces (clear), Lingual braces (applied to the back of your teeth) or Invisalign (virtually invisible and removable aligners that gently move your teeth into the desired position). I encourage anyone to seek a consultation if you want to straighten crooked teeth, improve your smile, or correct a bite - at any age.