"I am 5'2" and 27 years old. I wear clothes that are my size and avoid anything that looks like something my teen cousins would wear, but clients still think I am under 18, and it is affecting me on different levels. What can I introduce to my wardrobe to help me look more mature?"
This is a head-to-toe issue. It's as much about hair, makeup, and accessories as it is about apparel. A good haircut is the first step. Have a makeup consultation at your local department store. Make certain that you're wearing grown-up shoes and jewelry. You're petite, so be sure that you're not shopping in the juniors department. Finally, choose colors that are deeply saturated, like jewel tones, and avoid prints that are even remotely cutesy.