I am seeing leggings EVERYWHERE here, and on women our age and height. This is not just for young women.
I think the number 2 rule (after making sure your top isn't too short) is to wear BLACK leggings. Dark, opaque ones. It goes without saying that brightly colored leggings in pink look too young. But while other women may be able to get away with brown or gray leggings, if you are short and worried about looking age appropriate, I'd suggest sticking to black leggings only - just to be safe!
You need to play around with the length, but I personally think that a more grown-up version of this look is with a dress that hits just a few inches higher than the knee, instead of a tunic-length (mid-thigh). Of course there are going to be women who will blow this "rule" out of the water. But an inch or two above the knee is a good place to start.
Since you're petite, do try leggings with a sheath dress. Otherwise, once you get your leggings, just try them on with all the dresses in your closet! You may be surprised. I've discovered I have several dresses that work.
One thing I have yet to try is leggings with heels. I know Angie says this can work, but I'm dubious. The women my age that I'm seeing in leggings are all wearing ballet flats. It's the younger women who are wearing them with heels. But I am planning to try them with the cedar city wedges so we'll see.... I'm keeping an open mind!
So basically the rules seem to be ... go for modesty. Opaque leggings, a dress not a tunic, something with structure (like a sheath) or not too body hugging, and with flats instead of heels.
I do like that express top but not only is it too short, I would be concerned that the band is too booty hugging for leggings. Let the leggings hug your legs, leave the rest of the top more flowy with volume, or skimming with some structure. Make sense? I think this is why shirt dresses work so well with leggings; they add structure and in general tend to be a modest type look.