Makes you look OLDER...

A boxy, guy-style shirt tucked into baggy, pleated khakis doesn't do a midlife figure any favors -- the excess fabric just adds extra pounds. It's a bland, throwback outfit that says, "I found my look in the eighties...and I refuse to change!"

Makes you look YOUNGER!

Sleek but not tight, these flat-front stretch pants ($70, Loft) give you a slender line -- and the right-now color shows you're up to speed on the latest trends. Wear the slim cotton turtleneck ($80, Talbots) untucked for a relaxed, modern vibe.

Earrings, $90, Skinny by Jessica Elliot Cuff, $60, Kenneth Jay Lane; qvc.com. Shoes, $119, J. Jill.

Makes you look OLDER...

Proof you need to go bolder as you get older: The mushroom hues of this dowdy skirt and too-big tee have a way of making everyone look washed out. The cross-body bag is too sporty for the office -- and misses the chance to have some fun (think color or a curvy shape) with accessories.

Makes you look YOUNGER!

If you think patterned above-the-knee skirts are just for college girls...not so! This example ($118, Nic + Zoe, zappos.com) looks good and grown up when paired with a tailored denim motorcycle jacket ($138, Isaac Mizrahi Jeans; bloomingdales.com) and a complexion-brightening tee in cool mint ($32, WkShp, lulus.com). Adding polish: the curvy bag (Big Buddha, zappos.com).

Necklace, $78, Kenneth Jay Lane; qvc.com. Bag, $95, Big Buddha; zappos.com. Pumps, $69, Anne Klein; zappos.com.

Makes you look OLDER...

Tight and bright, this cocktail dress is trying too hard to look sexy, from the plunging neckline to the abbreviated hem. T-strap stilettos cut you off at the ankles, and the teetering heel height won't keep up with the pace of your life.

Makes you look YOUNGER!

This dotted sheath ($98, Line & Dot) shows you can dress flirty without flashing a lot of skin. The black-and-white color combo is sophisticated, and the swishy hem flutters with every step.

Mosaic hoop earrings, $83, Melinda Maria; melindamaria.com. Circle bracelet, $34, Guy and Eva; guyandeva.com. Pumps, $80, Aldo; zappos.com.

Makes you look OLDER...

Long and matronly, this shapeless skirt is about as flattering as a sack. Worn with a boxy cardigan hitting at the widest part of the hips and a pair of zero-personality flats, it's a confidence-zapping outfit that's way too geriatric for anyone under 101.

Makes you look YOUNGER!

Knife-pleated and swingy, this above-the-knee skirt ($168, Pendleton) shows off still-got-it legs. A lean violet cardigan ($21, Ami Clubwear) over an orchid satin tank ($83, Line & Dot) highlights curves -- and frames your face with uplifting color.

Necklace, $55, Marimekko; us.marimekko.com. Cuff, $148, Alexandra Beth Designs; alexandrabeth.com. Bag, $190, Iman Platinum Collection; hsn.com. Shoes, $168, Johnston & Murphy; johnstonmurphy.com.

Makes you look OLDER...

Mom jeans like these -- with a high elastic waist and a hip-expanding tapered leg -- have become a punch line for a reason. Also not helping: a no-waist blazer and bag that are too straitlaced for weekends, and clunky sneakers better suited to the gym.

Makes you look YOUNGER!

In a slimming dark rinse, bootcut stretch jeans ($110, NYDJ) are Saturday comfortable but look weekday chic. An up-to-the-minute color-blocked cardigan ($96, Ava; 212-719-9400) and padded-sole leopard flats ($86, Isaac Mizrahi Live; qvc.com) let your style sense shine.

Shirt, $64, Jones New York Signature. Bag, Eloquii by The Limited. Necklace, $55, Karen London; karenlondon.com.