Many agencies will sign you up with only 6 months of experience, but that doesn't mean they'll be able to place
you -- more and more hospitals are requiring 2, 3 or more years of experience (in a particular specialty). Hospitals pay a huge amount for travelers, and, for that amount of $$$, they expect to get a seasoned "pro" who is ready to hit the ground running and do the job with a bare minimum of orientation.
When you graduate and start working, notice how long it takes you to feel really comfortable and competent in your regular, full-time workplace. Then, think about how long it will take for you to feel ready to walk in and be able to function competently and independently in a new, strange work environment. When you get to that point, you'll be ready to travel.
Also, agencies are looking out for their own best interests, not yours. They will throw you to the wolves without batting an eye if it suits the company's needs. If you crash and burn, they have plenty of other warm bodies to take your place. You
, though, only have you
. In addition to simply being clinically competent, it's helpful to be savvy about nursing life in general to be able to protect your interests and your license, and recognize when you're being put in a dangerous situation and what to do about it, and that takes some time, also ...