I am 26, 5'7", 160lbs, 38a bra size. 600cc too large? (Photo)

Yes. 600 cc is too large. It may create a nice look, but you have excellent anatomy and a large implant will stretch your breasts, thin your skin and breast tissue, and cause more rapid sagging. There's no fix for these changes once they occur. Choosing the appropriate implant size depends on your breast dimensions and your goals.  Make sure you find a board-certified plastic surgeon who will speak with you about all of your options and give you honest opinions about the downside of overly large implants. 

Hi O,  600 looks like it would be pretty big for you.  If you want to go for it, inquire about the Ultra High profile. It would possibly be a better fit for the footprint of your breast. Here are a few tips for you because this is perhaps
the hardest decision for a patient to make, as well as the surgeon.  Also see the video attached to my answer.  We spend up to two hours for our BA consults
to be sure there is careful communication. We do a full exam in front of a
full-length mirror taking six exact measurements.    We
put your photos on a large computer screen for imaging, and go over your
“ideal-size” photos. We then save this information to your password protected
“web account.”
     First and
foremost the implant should fit the dimensions of your breast and tissue cover.
 Balancing the implant to your
over-all body shape and tissue cover is essential.    The main thing is to
have the diameter of the implant fit the diameter of your breast "foot-print".
 Higher profile implants tend to have a smaller diameter.  Higher is really a marketing term, but often
translates into the same volume implant with a narrower base.  Saline implants actually tend to decrease in
diameter as they are inflated!  The average size chosen over our last 7,000 breast implants was
“350cc”.  BUT, 90% of our patients tell us they wish they were
bigger a year after BA.  (We will see you
every year for routine checks at no charge.) It’s like your mind incorporates
the "new you" into your own self-image over a period of time. Cup size estimates can be misleading, but I generally advise patients
that they will experience an increase of approximately one cup size per 200 cc.
 You can try on implants in the office by
placing them into a special bra.  The implant is also flattened somewhat when under
the muscle, so it is a good idea to bump it up a bit. Approximately 1-ounce (25cc) is added to the final volume to account for
flattening of the implant in the partial sub-muscular pocket.  Once you decide on a size you like, then add
on 25cc, because in real life the implant will be flattened slightly by your
tissues.  Multiple measurements need to
be taken to fit an implant to your exact anatomy.  Have your surgeon's
office show you the charts of the implant dimensions for the various profiles
of silicone and saline from the manufacturer.  Then you and your surgeon
can piece together the puzzle by matching your measurements, with your wishes,
versus your tissue cover and the available implants to arrive at
a surgical plan.  Keep in mind
larger implants tend to have more problems over the years.  Since silicone implants wrinkle less than
saline implants, they might be your best bet.
     You can
also approximate this at home by measuring out an equivalent amount of rice
placed into a cutoff foot of old panty-hose, and put this in your bra.  Wear this around the house for a while, and
see what you think.  Implant size must
square with assessments of tissue cover, breast diameter, and chest wall width.
 Multiple measurements of your chest wall
are taken (seven in total).  Implant size
selection has been an issue of much discussion.
    
Therefore, I use a wide variety of methods, but the implant size is
always established preoperatively.  Also,
patients are advised to bring reference photos demonstrating their ideal size
and shape.  A photo album of patient
pictures is maintained to assist them.  These photos ultimately help in determining
where the implants will be placed, since they can be shifted inside (to provide
more cleavage), to the outside, up or superiorly, and down or inferiorly during
surgery.  In determining the final size
selection, I always place the highest priority on the preoperative measurements
and potential tissue cover.  Finally,
your verbal requests are factored into the analysis.
     We use
the quick-recovery approach, so click on the web reference link below to have
this explained and you can see the list of Quick-Recovery (Flash-Recovery or
Rapid-Recovery) Breast Augmentation articles from peer-reviewed surgery
journals.  It is a surgical procedure that
uses special instruments and techniques to minimize tissue damage and avoid
touching the ribs. It causes far less trauma to surrounding tissue than
traditional approaches, and it dramatically reduces pain and recovery time. In
published studies of BA patients, 95-percent of women interviewed after the
procedure returned to normal daily activities within 24-hours. Quick-recovery
BA is not a “gimmick.”  These specialized
techniques, which actually speed recovery and get you back to your daily
routine, kids and work, are published in our plastic surgery journals.  Because these PS journals are “peer-reviewed”
and edited, they are the gold-standard in our field as being valid science.
Therefore, these are sound techniques, not marketing hype. 
     Be sure
to see only a board certified plastic surgeon (by ABPS - The American Board of
Plastic Surgery) who is a member of ASAPS (The American Society for Aesthetic
Plastic Surgery) and or a member of ASPS (The American Society of Plastic
Surgeons).  Also, ask if the PS has an
established, high volume breast augmentation practice, performing several
hundred breast augmentations each year.  Be sure the PS has been in practice for a
while, about 20-years might be a good gauge. 
Does the PS offer all three incisions? 
Discuss the implant type (gel or saline), shaped "gummy bear"
or non-shaped, smooth or textured, implant pocket (over or under the muscle)
and the "quick-recovery approach." 
Ask to see their before and after photos if you didn’t see any on their
website.  If they are experienced, they should have several 100 breast
implant patients for you to view.  I would also recommend that your doctor
offer you the chance to talk to past patients who would be happy to discuss
their experience with you.  You need to feel comfortable, so make sure the
environment is safe as in an accredited surgery center.  Also, ask a prospective surgeon if he or she
has ever published journal articles in professional peer-reviewed journals,
which they can provide you.      
All the best, “Dr. Joe”
 
 

Thank you for your pictures and questions. Although I do not have your breast measurements, I am going to take a guess and say that you breast width is around 12-13 cm? That being said, I think that a 600 cc implant is very large and I would caution you that it might be too big for your frame. I think the only way to get an implant that large in you would be to use a very high profile implant and this would give a very augmented and unnatural look. If this is the look you are going for, then that is your choice. But if you are interested in a natural look and a pleasant aesthetic outcome, I would suggest you have a consultation with a local board certified plastic surgeon and try on some sizers to get a better idea of what a reasonable implant might be for you.Hope this helps!