Is a small rough patch of skin always Actinic Keratosis?

AK is a premalignant condition usually seen in middle aged to elderly individuals who sit in the sun. I would be surprised if you've been affected at only 19, but anything is possible. However, its far more likely this is just a patch of dermatitis. Try some simple emollient cream or a cream containing a tiny bit of steroid (very small amount - don't apply strong steroids to your face) - your pharmacist can help. If it doesn't settle in a couple of days, see your doctor.