Do you really have to sign up for the military for 8 years?

That is SUCH a long time. I'll be 26 by the time I retire, and that's if I'm lucky to go to boot camp right at 18. That's old lady to me. I was thinking they had a minimum of 4 years, but it said 8! What do you do when you are in IRR? Can I have a normal life while in it and do what I want, such as hold a normal job and travel... Civilian stuff.