Everyone is genetically different. Some people have more facial expressions than others. So its hard to give an age to when you should start Botox. You could try it now and see how you like it. Botox results take up to 1-2 weeks and last up to 3-4 months in new areas of treatment. See an expert. Dr. Emer
Technically, 19 is not too young to start Botox. However, in my opinion you should refrain from doing any cosmetic treatments until you are older. I'm sure that you are a beautiful young lady that is not in need of any cosmetic treatments.