After further review, it seems that even though Jennifer Lawrence might believe she had an imposter butt in a photo of her in a bikini, the “90-year-old butt” is indeed her very own toosh.
Here she is explaining to Dave that she is NOT the owner of the butt in a photo taken of her while in Hawaii:
A close up of the photo in question:
This is the original, undoctored, straight-from-the-photo-agency version:
Image by Splash News
Here is the "90 year old butt" (left) with the real butt (right):
