Is 17 too young for breast reduction surgery?

I have asked several Ob-Gyn doctors about breast development and the answer I have gotten is that breast development is usually complete 2 to 3 years after the onset of your period. So, in your case, a breast reduction seems like a reasonable option.

One month ago I performed a breast reduction on a 17
year old woman with a situation similar to yours.Her mother and her had been discussing it for
years and finally agreed to go ahead with surgery.She suffered from neck, back and shoulder
pain and could not participate in physical activities at school.I recommend a new technique called The
Horndeski Method™.The weight of the
breast is transferred to the underlying muscle resulting in immediate pain
relief without excessive reduction.The
breast tissue is reshaped creating upper pole fullness, elevated higher on the
chest wall and more medial to increase your cleavage.This technique avoids the ugly vertical scars
of the traditional technique, maintains nipple sensation and the ability to
breast feed.Best Wishes,Gary Horndeski, M.D.

I'm sorry to hear about the physical and 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 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 am glad you have the support of your mother as you do your homework.It will be important that you learn about the potential risks/complications associated with breast reduction surgery. Unsatisfactory scarring is one of the potential complications. Make sure you also understands 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.  Best wishes.