Will saline implants look fake on me if I’m skinny?

hello thank you for your question and provided information as well..Based on your question, it is difficult to evaluate if the case does not have photos to give you an official evaluation, my recommendation is that you be evaluated in person by a certified plastic surgeon.

Good question. Much of the final look and feel achieved after breast augmentation surgery depends on several factors:
1. The initial shape, size (volume of breast tissue), symmetry of the patient's breasts. In general, the better the preoperative breast appearance the more likely the breast augmentation “look” will be optimal. 
2. The experience/skill level of the surgeon is important in determining the final outcome. For example, the accurate and gentle dissection of the breast implant pockets are critical in producing long-term well-placed breast implants. I personally think that these 2 factors are more important than any others, including type (saline or silicone) or model (low/moderate/high profile) of implant.
3. The type of implant used may determine the final outcome, especially if the patient does not have significant covering breast or adipose tissue. For example, some surgeons feel that silicone implants have a more natural look and feel than saline implants because silicone gel has a texture that is similar to breast tissue. In other words, if a patient has very low body fat and/or very little breast tissue, the silicone gel implants may provide a more "natural" result. All FDA approved breast implants utilized today are cohesive gel silicone breast implants;  some are firmer than others (including the true "gummy bear" breast implants).  I find that I use round smooth silicone gel breast implants for the vast majority of patients who seek breast augmentation surgery.In my opinion, there is no good reason why there is an FDA mandated age of 22 for patients to receive silicone breast implants. There are many patients under the age of 22 who would ( based on their body type and the advantages of silicone breast implants) benefit from the use of silicone gel breast implants. Therefore, I find that I DO use silicone gel breast implants for patients under the age of 22 frequently. 
4. The size and model of breast implant used may make a significant difference in the final outcome. Therefore, it is very important to communicate your size goals with your surgeon. In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. I have found that the use of words such as “natural” or “C or D cup” etc may mean different things to different people. 
Also, as you know, cup size varies depending on who makes the bra; therefore, discussing desired cup size may also be inaccurate.
  To summarize: select your plastic surgeon carefully. Communicate your goals carefully as well.  Chances are you will be very pleased with the outcome of breast augmentation surgery. 
I hope this helps. Best wishes. 

When the silicone gel implants came back on the market, the FDA set a 22 years old guideline for their usage in cosmetic cases.  However, they were approved to be used in under 22 year old patients for “reconstruction”, which can include severe micromastia (small breasts), severe asymmetry, or congenital defects.  They are used all the time in under 22 years old patients simply as an off label use without any problems.  For me, the silicone gel implant is a far superior device compared to a saline implant, and if the patient would benefit more from a silicone implant, then I use them regardless of age and have many patients under 22.  The best thing to do is to have a consultation or two, even if it means driving outside your immediate area if need be.  I hope this helps.