You have a young face and body, which guys love. That works to your advantage while dating. Just make sure that when you are talking with guys that you mention you are in college so they know you aren't as young as you look. You might scare off some guys who think you are too young. Make sure you point out your actual age to improve your chances.
As for in the professional sense, dress in a more conservative fashion and you'll be seen more as an adult.
Little girls can still be taken seriously, you just have to act your age, have good posture and let people know you aren't a teen, even if you look like one.
I suppose you could wear your hair shorter, this would add a little to your apparent age. You could practice scowling a lot , the women here in the US do this and it makes them look older because of the wrinkles it causes, but your smile is so nice, it would' t be worth going to all that trouble.
Of course you could dress more 'maturely', wear sedate clothes, no miniskirts or manga style things. A necklace, all by itself, adds an adult panache to any outfit.
Soon enough you'll regret complaining about looking so young!