Birthday cut offs for starting Kindergarten vary from state to state. Some have a Sept. 1 cut off while others have a Dec. 31 cut off. It is best to check with your local school district. Most of the time this information can be found right on their website or you could probably just call the nearest elementary school to your home.
If the cut off date is Sept 1 and your daughter would have to wait another year but you feel she is emotionally and academically ready, then you can ask about testing. If she passes the test, they will allow her to attend Kindergarten. Once again, check with your local school district.
Keep in mind that if your daughter attends Kindergarten and her cut off is after the date set by the state that she will always be the youngest in her class. However, if she waits, she will be one of the oldest. Seriously think about her emotional and maturity before making a decision before having her tested - if that comes down to it.
The good news is you have a whole year to do some research on the topic in order to form your own decision.