If you're only 18, going to college and getting a bachelor's degree isn't such a bad thing in general, not only for expanding your knowledge in a wide range of areas (which will make you a more well-rounded citizen and artist) but it can help with applying for certain jobs over the years, especially if the film industry career doesn't pan out.
No, it's not essential for becoming a cinematographer, though my career advanced at first because of industry connections I formed at film school. It's a useful intermediate stage, especially if you are a film student in a production friendly city.
I went to film school when I was 26, as a Master's Degree student, and got out at 29. But I had been shooting my own stuff since I was 15 and already knew a lot about shooting at 26 a decade later, so film school wasn't so much about me learning about filmmaking as it was a time for me to figure out just how to enter the professional world. I felt a little bit lost before that, even though I had actually shot some minor stuff for pay before film school.
In general, though, I'm not so keen on 18 year olds becoming professional filmmakers without some life experience and academic background behind them, and some maturity, but I'm sure some 18 year olds here will disagree...
The appeal of college isn't so much about film training, it's about learning in general -- about literature, anthropology, history, languages, sciences, whatever. That stuff will enrich the rest of your life, both while you are making films and definitely when you are not making films. I have an English Lit BA degree from UCLA which I cherish very much, perhaps more than my Masters in film.