I am a 16 year old girl. My breasts are size 32DDD. Is breast reduction surgery a good idea?

Not only do you have large breasts at an early age,
but you’re already suffering from significant symptoms. I generally prefer to
wait until the breasts have stopped growing before proceeding with breast
reduction, but in your case early intervention may be appropriate because of
your symptoms.I
recommend a consultation with a board certified plastic surgeon.Obviously, your parents need to be involved
in the process as well.Breast reduction
has significant benefits and patients who undergo the procedure at an early age
experience the benefits over a lifetime.There
are downsides as well.These include the
potential inability to breast feed, prolonged healing, decreased nipple
sensation and scarring.In my
experience, patients who undergo breast reduction at an early age, not only
experience relief of their symptoms but also an improved quality of life.

If you are having physical and emotional problems because of the size of your breasts and you and your family agree, then it is a good surgery for you.

I recommend that you see a Board Certified Plastic Surgeon who specializes in breast surgery for a consultation. You will learn all the pros and cons of surgery at your age. There are many benefits that you are already aware of. If you haven't finished developing there is a chance you may need a further reduction in the future. Depending on how the surgery is done, it may compromise your ability to nurse, and nipple sensitivity may be reduced. Most girls and women are thrilled with their results and only regret they didn't do it sooner. But you are the only one that can decide if it is for you. Good luck!

If you are 16 years old and your breasts are still growing then if possible you should wait until they are no longer growing for the most predictable results. Existing breast tissue can become larger after a breast reduction even if you haven't gain weight. A few of the more common reasons (besides weight gain) are use of hormones like birth control pills (even changing types) or others at the time of menopause, endocrinological problems, further normal growth if the first procedure was done at an early age, pregnancy related, and in many cases unexplained reasons. A secondary breast reduction can be performed once the cause is understood.

I'm sorry to hear about the physical and (possible) psychosocial problems your disproportionately large breasts are causing you. 
It is probable that you are dealing with juvenile breast hypertrophy along with the physical and psychosocial consequences of this diagnosis. In other words, the breasts are too large for your frame causing  both physical and (possibly) psychological distress.
In my practice, timing of breast reduction surgery is determined on a case-by-case basis. It is not too early to do your homework and learn as much as possible  about  breast reduction surgery and the potential risks and complications associated with  the procedure. I'm glad you have the support of your parents as you do your homework.
Unsatisfactory scarring is  one of the potential complications. Make sure you also understand that further surgery may be necessary in the future (for example if the breasts were to grow in size again).
On the other hand, breast reduction surgery is one of the most patient pleasing operations we perform and I think that for the right teenager (enough symptoms) it may be an excellent option (regardless of the age).
Sometimes breast  reduction surgery is covered through health insurance. The best way to obtain insurance coverage for breast reduction surgery involves some “hoops” to jump through. The more documentation you have (for example, from your primary care doctor, physical therapist, chiropractor etc.) the better when it comes to obtaining insurance “authorization” for the procedure.
This documentation and letter/pictures from your plastic surgeon will help you obtain authorization.
 When the time is right,  seek consultation with well-trained/experienced board-certified plastic surgeons.

I hope this,  and the attached link, helps.

Good question, and more common than you think. Yes, reduction is a great idea for a younger patient but not until the patient is sure there has been no change in breast size for a minimum of 12 months. It is also necessary for a parent to agree and for the young patient to realize scars are forever, breast feeding ability may be compromised and sexual sensitivity of the nipple area may be lost forever.