I'm 38. I feel your pain. The grey hairs, the crow's feet wrinkles, it all sucks! However, I don't feel old. I worry about the fact that I'm not as successful and ahead of the game I thought I'd be at this age. But I do things to still hang onto feeling young.
The clothes. Like you mentioned, hanging back on style can really age a person. Dress young! Don't be shy. It's something my friends admire and it inspires them to dress younger. I shop in the "misses" section all the time. I keep up with the shoe styles. I still dress pretty conservatively- you won't catch me in a low slung top and short skirt! I don't have much money to work with, so I don't shop high end brand names. But I find you don't really have to in order to keep up.
I use the "age defying" products. They actually do work! Loreal Hydra-renewal moisturaizer after I wash my face. It makes a huge difference from the times I forget to use it! Dry skin is the worst in making a person look older. Moisturize!
I don't do make-up. Just my preferrence.
Hair. I keep my hair "cute." Not over the top or anything. It's just past shoulder length, loose curls and usually I follow the basic trends in what I do with it. That said, I do not spend a lot of time on my hair! When the grey starts to get obvious, I definitely plan to start dying it. Bit it boggles my mind that women my age wear these short, layered old lady hair styles. WHY????
If you have a young or favorite part of you- nice legs, pretty eyes, cute nose or whatever, focus on it somehow.
Lastly, try not to think about the years you've lost. Try to think about the things you want to be or do in ten or twenty years. I love the saying, "It's never too late to be what you wanted to be." Seriously! Always wanted to learn piano- go for it! Ballroom Dance- look at Mary Murphy, at around 50 years old and still winning awards and highly acclaimed! There are so many inspiring successful women our age. Do some google searches - it may just boost your mood around being in your 30's.
Also, smile, do young things- ride a bike, blow bubbles, fly a kite, get a puppy, sing with abandon to your favorite songs, play board games, go to a penny-candy store. It's all still just a fun as it used to be! And laughter keeps a person youthful.
Hope this is useful to you. Best wishes!