Join a riding group if you can. You will have others around for help answering questions but also incase anything happens to you or a member of the group you'll have witnesses. You can also use a buddy system should someone get a flat tire or fall down (sand/oil on road, etc.).

Having a bike could also be a way to get to work once you start working. You could keep in shape as well as saving on gas, insurance, repairs, etc.

Bicycles serve as a great form of therapy too. You can go for a ride and unwind. And let's be honest, if you really wanted to stay safe you'd have joined a knitting club. Cars and bad drivers are part of the sport. So are cuts and falls. You just have to be aware of your surroundings and be street smart.
Furthermore, you want a bicycle. Not a hand gun. You aren't out defacing public property, robbing the elderly or selling Crack to 5 year olds. There are many far worse choices you could make about how you want to spend your time. Growing up as I got into downhill racing this was something my parents and I both agreed on. Friends and family would realize how much time and money I had invested in bikes and they would be awe struck, as if I had 3 heads, until I reminded them there was far worse I could do. As I told people: My bikes are your classic cars, your Sunday golf, your card collection, yes it's not popular but it's what makes me happy and keeps me free.

Good grades help also. By my senior year in school I was taking AP and Honors courses and I was still straight A's.