40 yrs old - I want a BBL. Will I get good results?

Hello! Thank you for your question. Since you have already had a Tummy tuck with Liposuction it may be difficult to achieve the results you want for a Brazilian Butt Lift. You may not have good quality fat to transfer. It is impossible to say without an in person consultation to assess you. I highly recommend seeing an experienced board certified plastic surgeon to discuss your concerns and goals of surgery. See the below link for more information on good candidates for surgery and internal VS external fat. 

Thank you for your question and photos. Based on these photos, you are a great candidate for VASER Hi Def Lipo 360 degrees (abdomen, pubic area, whole back, lower back fat pad, waist, hips and anterior and lateral rib cage) with fat transfer to the buttocks for shaping and enhancement. It seems you had a "standard" tummy tuck with poorly placed scar which is too high. This could be lowered down to below the pubic hairline level at a later date. I do these surgeries in our accredited office surgery suite under intravenous sedation.See a board certified plastic surgeon experienced in advanced body sculpting techniques for an in person consultation/evaluation. Good luck.

Thanks for the question. 
In this regard, I recommend you waist and back Liposculpture, getting better curves especially in the waist, improving your body contour.
Finally, I suggested take the fat we get and transfer to the buttocks and hips, to mold them and get better volume, contour and butt projection, is that we know as "Brazilian Butt Lift" (BBL).
Kind regards