Can my saggy flat butt look large and natural with butt implants? (Photo)

Allow me to answer your question as best i can based upon your photos. However, please keep in mind that an in-person consultation with physical exam is first necessary before any legitimate evaluation or final surgical recommendations can be made. On a very positive note, it sounds as though your desires and expectations are very realistic and in-line with what buttock implants typically can achieve (i.e. a proportional, tastefully contoured, and perky athletic buttock). Glad to be of help. 

Dear madam,   Thanks for posting your pictures. From observing your pictures and height information, you will be a great candidate for 435 cc  or 565 cc (according to your desire) , oval round ultra soft silicone  implants, placed in a sub fascial pocket (on top of the muscle) through a single low incision between the cheeks. I have operated on over 600 patients using that technique, with very high satisfaction  by the overwhelming majority of them.    You have to realize that not all results are the same, because there are different implants and different techniques. Also, experience,  technical skills and aesthetic eye are critical for good outcome. So, do your due diligence carefully and choose your surgeon wisely, to avoid bad result and need for corrective surgery that will double the cost and recovery time.   Always, consult with experienced board certified plastic surgeons who operate in accredited surgery center for your safety. Most importantly, check the before and after pictures in the photo gallery, to make sure that they are numerous, consistent and attractive with nice 'S' curve, nice projection, round hips and natural look.                            Best of luck,                                        Dr Widder                                                 

Implants should be placed within the muscles for better long term results. The key to this surgery is to select an implant that is not so large that the muscle cannot cover it reliably. You want a nice result, but you want to avoid the complications (need for removal, infection, extrusion, fluid collection, implant migration, and implant visibility, among others). Studies have demonstrated that sizes above 350 cc have a greater rate of complications.
Schedule an in-office consultation with a board certified plastic surgeon with ELITE credentials (board certification, experience, training, education, favorable patient reviews, and untouched before and after photos in his or her gallery on the website) who performs hundreds of these procedures annually. During your exam, the board certified plastic surgeon will measure you and determine the best size to suit your anatomy.Kenneth Hughes, MD, Board Certified Plastic SurgeonLos Angeles, CA

Based on your photos and the amount of skin excess you have, you can achieve great results by getting a BBL or a butt augmentation. 
Thank you for sharing your photos. 
I hope my answer will help you to your question.
Before undergoing any surgical procedure, please seek a board certified plastic surgeon

Dear BreastButt2017,Awesome job!  You have seen the payoff of a good weight training program just 6 months into it.  In the realm of exercise training to build muscle mass 6 months is really a nanosecond (exaggerated).  If you have received such great results in that short a time, it makes sense for you to continue on what would be considered a much healthier and less risky way to augment your buttocks.  The $8-10 thousand dollars that you would spend on gluteal implants will buy alot of personal training.  Good luck!