Joining any branch of the military will be a good move. I went through college straight out of high school and really wish I had enlisted first.
It will make you more responsible and mature. If you decide to go to college after, you'll be much better prepared, not to mention it's pretty much paid for.
It might seem like 4 years is a long time, but it will be over before you know it. If you really like the military, you can get a college degree, become an officer and make a career out of it. Going in at 18 means you can retire at 38 with a pension and benefits, which would be pretty amazing.