The pitfall to dressing for special occasions is that women on either end of the age spectrum look wrong if they dress their age: in froufrou dress, young women look ready for prom. More mature women look mother-of-the-bridish in outfits that are deemed "appropriate" for their age group.
Younger women like Scarlett Johansson can carry off classic Hollywood glamour girl looks like platinum hair, lush red lips and form-fitting gowns. In a grown-up dress, a younger woman looks sexy.
Over 40-women can take a cue from Jane Fonda and stick with soft, modern hair (stiff updos look frumpy on mature women) and updated dresses. That doesn't mean they have to dress too young by flaunting ridiculous oversized tattoos like Melanie Griffith or wear microminis. It does mean that the dress should show some skin, even it's only a peek of a shoulder or an arm. Long sleeves, long dresses and high necklines age every woman.
