Are my Breasts Fully Developed?

Although breast growth varies from patient to patient, it generally stops between 16 and 20 years of age. Even though growth stops, the breasts continue to undergo changes for the remainder of a woman's life. This is effected by weight gain , pregnancy, lactation and gravity.Since you haven't experienced breast growth since you were sixteen, it's probably reasonable to consult a plastic surgeon for breast augmentation. At this point, your breast size is probably stable.

In general, female breasts stop developing at around 18 or 19 years old. This is when a primary level of maturity is achieved, however further changes occur with pregnancy and lactation (the production of breast milk). Your breasts will continue to change throughout your life, as the signs of aging become more apparent. For example, your breasts may begin to droop as supportive tissues weaken, or grow larger when you gain weight. Sagging is common after childbirth. For this reason, if you are planning to have a child soon, it's best to wait until after to proceed with breast augmentation.

Yes, in agreement with other responders, your breasts are fully developed but change during your adult life in response to weight and hormone fluctuations, most notably during pregnancy, lactation, and afterward.  If size of breasts are a hangup, go for consultation(s).  Augmentation, if performed by a qualified surgeon who properly selects and prepares you, may be the best investment you ever make.