As discussed in other answers, for cosmetic breast augmentation (not breast reconstruction such as asymmetric breasts) you must be 18 yrs old for saline implants. The FDA has approved the use of silicone implants, but you must be 22 yrs old. So now as an adult, you have an important decision and should evaluate all the options. If you do not have a lot of breast tissue, silicone implants generally give a softer more natural look.
Silcone implants have undergone intense study and have been proven to be safe. You need to discuss all of the risks and benefits of each of these devices with your surgeon. But you need to decide if it is worth it to you to wait 4 years before undergoing the procedure? Also understand that breast implants are not a lifelong device. As you get older, your breasts continue to undergo the aging process. So it is very likely that you will need an exchange of the implants, with or without a breast lift.
There is no correct answer. The most important thing is that you get all the information and feel good about your decision. Maybe you can even educate your family and friends and they will feel better as well. Good luck.