Short answer is NO....best and most dramatic (and reliable) results are achieved with a Mastopexy or breast lift procedure. Excess skin is removed and the breast tissue is rotated and elevated to a higher position on the chest wall therefore rejuvenating the shape of the breast and the position of the Nipple Areolar Complex (NAC).
Sure, Thermage can be used for sagging and excess skin on the breast, but I can almost guarantee you that your results will be minimal (if your goals are to rejuvenate your breasts).
I do recommend you seek out a Board Certified Plastic Surgeon to consult with....he or she will evaluate your breasts, the sagging of the skin and breast tissue, and give you the best advice.
Hope this helps!
Dr. C