A: It’s an odd request, but it’s a valid one.  Looking more mature will not only reduce the "how old are you?" questioning, but it’ll also help you to be taken more seriously at work.  We have a few quick tricks to add age to your look:

Balance out your Round Face:  I’m guessing that the youthfulness in your face comes from a round shape; the rounder your face, the younger your look.  To counterbalance the roundness, look for geometric shaped earrings, pointed collars, and more angular clothing.

Wear Structured Clothes:  The more structure in your clothes, the more mature the look.  I’d recommend building your wardrobe around tailored garments and accessories - double breasted coats, belts, blazers, and other fitted items.

Drape Yourself in Jewel Tones:  Bright primary colors are youthful looking, but deeper jewel tones like emerald or turquoise are more refined.  Neutral colors will also add to the maturity of your outfits.

Wear Makeup:  The key here is to wear makeup that’s not too heavy.  Try makeup that’s sophisticated, like a soft smoky eye for evening.

Slip on a Pair of Heels:  Since you’re only 5 feet tall, you’ll also benefit from a couple of inches of extra height.  Height will help you add years to your look, especially if the shoe is in a sophisticated style.