While age and experience has a lot to do with why my rate has climbed so high and so fast, mostly it is due to confidence. You have to ignore your inner critic that says you are not worth $12/30/50/75 an hour, and honestly consider what your time is worth. Would you trade an extra hour of sleep or an extra hour with your girlfriend for the price of a meal at Chili's? A tank of gas? A shitty coffee table at Ikea?
There's a spectrum there, and you have to place yourself as high in the spectrum as possible. Don't stop going higher- even if people laugh at you. Two days before I landed my first gig at $75 an hour I had a recruiter laugh at me and that rate. Ignore them. Trust yourself. Trust your abilities. Charge a good price for your time. Because after all, time is all we have. Make them pay for it.