I'm only 18 yrs old, but my breasts are already up to a 34L (UK sizing). How long should I wait for a Breast Reduction? (photo)

Breast reductions are wonderful procedures and some of my happiest patients are my breast reduction patients. At 18 years of age, you should be just fine getting the procedure done.  Many patients experience immediate relief of neck and back pain. Even more, this procedure is typically covered by insurance!  Thanks for your question.Dr. SchreiberBaltimore plastic surgeon

There's not a rule regarding how young is too young for breast reduction surgery, but your breasts should have finished growing first.  At 18 years old, your breasts are likely finished growing with the exception of changes that may occur as a result of weight gain and pregnancies.  Your photo clearly shows that your breasts are quite large and it's not surprising that you're having shoulder and back pain as a result.  I suggest that you see a plastic surgeon now to discuss the procedure and the pros and cons of having the surgery in the near future.  Having a breast reduction can be life-changing and many women say their only regret is that they didn't do it sooner.Best wishes

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.   For example, 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.