A BBL may be able to improve your shape, but from your photos you appear relatively lean with limited donor fat. That usually means the result would be more of a modest, natural improvement rather than a very large increase in buttock size. Often the biggest change in lean patients comes from shaping the waist, flanks, and lower back, not just from how much fat can be added to the buttocks. Tight skin and stretch marks do not automatically rule out a BBL, but they do affect expectations. Tight skin can limit how much fat can be safely placed in one session, because overfilling a tight envelope can compromise fat survival and contour. Stretch marks suggest the skin has been stretched before, but they do not tell the whole story; your surgeon has to feel the skin and assess elasticity in person. If you want a subtle improvement in roundness and hip/buttock contour, you may be a reasonable candidate. If you want a dramatic change, you may be disappointed or may need more than one fat grafting session. I would meet with a board-certified plastic surgeon who performs BBLs regularly and ask specifically how much donor fat they think you have and what percentage of your goal is realistic while keeping fat placement safely in the subcutaneous plane.