Please consult your parents first to see if it is alright for you to have a cosmetic procedure at this age. If your family is supportive and it is something that you want to do then please find a board certified dermatologist with a great deal of experience with these injections.
First, any procedure you undergo would have to be consented to on your behalf by your parents. Would they be ok with this? Would they consent to let you have treatment? Second, if you get filler will you become obsessive about it? What if it's not exactly how you thought it would be? There are a variety of things to consider here and I wouldn't necessarily be focused on your age with it, but the reasons you want the filler, and what you would do if it didn't work out the way you might be thinking it would. Sometimes "fixing" one thing creates something else.
"This answer has been solicited without seeing this patient and
cannot be held as true medical advice, but only opinion. Seek in-person
treatment with a trained medical professional for appropriate care."
the label on Restylane notes it's safety has not been demonstrated in people less than age 22...a more important issue is whether other people agree that you have a lip problem...at least from your photo it looks like your lower lip is normal...sometimes people fixate on areas and believe a problem exists when in reality the problem lies elsewhere...if you really think your lip is abnormal and your parents or friends agree, then talk with a dermatologist or cosmetic surgeon and see what they say...but don't be surprised if they want you to talk with your family doctor about why there's a confidence issue
From your statements and viewing your photo, thin lips look to be hereditary in your family. You might want to use a filler in your upper lip, such as Juvederm or Expressions to see how you will like the result. If you are happy with the result, you might want to think about a permanent solution, such as PermaLip. Do your research,
find a good Board Certified Plastic Surgeon for a consultation and with this knowledge, you will be able to make
the decision which is right for you. Good Luck!