High blood pressure.?.?.?

Hi i am an 18 year old male. I am not over weight and I exercise alot. I am also a firefighter. When I turned 16 I started to eat very bad alot of junk pizza salty foods ect. At around 17 I was told i have high bp. I had my bp taken at the firehouse and it is 180/75. I do not have any other problems besides bad eyesight witch runs in the family but glasses are coming in but thats no problem. I am in the Marine Corps academy and they told me to change my diet asap no salty foods, soda, ect. Ever sense i been alittle kid i been eating that kind of food. What do you think is the cause of this and would my diet change it? I want to keep the medication as a last resort. ... thanks