What should i choose as a career?

im about to get my diploma and i want to become a radiologist. i want to because ive always been interested in the medical field and science. what would be good to major in college and how hard is med school? what will i be taking in med school? just throwing this out there kinda sad, no one in my family has a college degree or good career i will hopefully be the first. im 20 taking online classes to get my diploma . if i do good in college pass the mcat then get into med school im good right. do you think 20 is to old to start college? am i in way over my head? just be honest idc