If you want to look older there are several things you can do:
1. Stop wearing your hair in a ponytail and invest in a trendy, yet sophisticated, hairstyle. Look for pictures in magazines and tell your stylist you want to look older. You might go for a shorter hairstyle, which tends to age people.
2. Wear makeup. Play up your eyes or your lips, but never both at the same time. Make sure you always wear mascara at the very least & a swipe of gloss. If you want to go dramatic, try a deep red lipstick, but don't make up your eyes too much. A swipe of mascara will do you. And try putting it on your top lashes only. Makeup will help "age" you.
3. Dress like a 22-year-old college graduate. OK, you're a few years away from being 22, but still when you're not going to dance classes and you're going out with friends or shopping, dress like someone with a desk job would. Try heels, a sexy, but sophisticated skirt and a cool jacket.
4. Invest in Lucky Magazine. Lucky is a great magazine for stylish young people (and people in general). If you want to know what the hottest trends are, invest in this magazine, start studying the trends and adopt them.