If you had a specific use in mind (like a caption, a story, or a description), let me know and I can help you tailor it further.
To provide you with a "proper" or more polished version of that phrase, the best choice depends on the context you're aiming for. Here are a few ways to refine it: older mature mom booty
"The full, mature figure of a mother."
"The graceful curves of an experienced woman." If you had a specific use in mind
"Celebrating the timeless beauty of a woman's silhouette." Direct/Refined: "Mature feminine curves." or a description)