Well, apart from excellent make-up artists, skin care regimes created specifically and exclusively for her by the best available dermatologists/make up artists and, of course, people who excel in doctoring photos before we get to see them, having no worries and tensions also play a big role in keeping aging at the bay.
P.S. to me, she does look her age. No matter how matter she tries to look younger or the same age as Abhishek, she does look older than him. Now, this doesn't mean that she looks old hag or anything.