Kids start soccer at all ages. At the end of the day, it's running and kicking a ball. Lots to develop to be competitive, but not lots to learn to be able to just play.
In most communities, recreational soccer is a fall sport - that's when most kids play. In many communities, there are smaller programs in the spring and summer - some of those are for really competitive kids who go to tryouts, etc. but many are just to have fun, develop skills, and provide fall soccer kids who don't want to play a spring sport something to do in the spring and summer.
Check the website of your communities soccer league for info...if they're running any spring or summer programs, that's where you'll find the info.
If you can't get her into a spring program or summer clinic, just enroll her for the fall and have her play with her friends over the summer to get comfortable with the ball and the basics of how to play and she'll be more than ready for fall.