At 18 years of age your breasts are probably as developed as they are going to be and you could consider breast augmentation. When the FDA approved silicone implants in 2006, for no good reason, they recommended a minimum age of 22 before they thought a woman would be "mature" enough to make the decision about silicone breast implants. Most surgeons think this is bogus reasoning but are afraid to place a silicone implant in people under age 22 since it would technically be not "FDA approved". As a physician, we often do things that are "off label" and not "FDA Approved as long as this is disclosed to the patient. Someone who is as thin as you should be very cautious about getting saline because you will have a much higher chance of rippling.Seek consultation with a plastic surgeon who is certified by the American Board of Plastic Surgery who specializes in cosmetic plastic surgery, as evidenced by membership in The American Society for Aesthetic Plastic Surgery. Ask to see many pre and post op photos and speak with previous patients.