Send me a photo of it, I'll judge for you.
I have a very full butt too, so I've Googled this question before.
First, loose skin from weight loss often still contains a bit of fat. As you lose that remaining fat, the look of the skin will continue to look smoother. Second, saggy skin is a fact of fat loss. The good news is that reabsorption happens but it is a slow process, on the scale of 1-2 years (according to professional advice). Although you have to keep with your training program, I think it is a worthy goal to attain in and of itself. I think these are things that you have some control over.
But there are factors outside our control. For one, it should not be surprising that the shape of butts vary, and especially keep in mind that different races allocate their body fat in different ways. So, don't let images in the media overly influence your perception of what is good-looking versus what is normal. Another big point is that sagging is just a fact of aging. But looking at pictures of older bodybuilders, their skin is quite tight. Still, in the end who cares? Unless you're after guys way younger than yourself, I don't see why that is a problem, in the big picture.