Like these stars you posted here, they look young, they can wear young clothes. But even for them, they may only look young in photos, you know photos can lie. If you really meet them in person, you may realize they don't look that young anymore, the young clothes may not suit them so good.
The original post is about a real, not famous, face to face person, you can not compare her to those celebrities, specially, you did not see that person face to face and you have not met the celebrities face to face.
If you really think the 40yr can look good in 20yr clothes, try with a ordinary person, like yourself maybe...