How old does one have to be to have a breast reduction procedure?

No specific age. The youngest breast reduction patient I have treated was 15. She had so much neck pain that her pediatrician had obtained an mri, concerned that her symptoms were caused by a ruptured cervical disc. In fact, they were from the weight of her huge breasts. This, however, is unusual. Most breast reduction patients are in their mid 20s at the youngest.
No Specific Age. There is no age restrictions (low or high) for breast reduction surgery. Every patient's situation is evaluated on an individual basis. There are teenagers who present with juvenile breast hypertrophy and suffer greatly, both physically and psychosocially, from disproportionately large breasts. They may be excellent candidates for breast reduction surgery, regardless of their age.
It DEpends. Normally the earliest is after the breasts stop growing, at least 2vyears post menarche, or after age 18. Whichever is latest.