According to the Beal Early Childhood Center, some basic indications that a child is ready for kindergarten include being able to socially separate from the family for a while, and being able to share. Academic readiness markers include interest in letters and listening to stories. Motor skills include being able to zip or button his, or her, own clothes. Education.com offers a handy kindergarten readiness checklist for parents.
Regardless of the age at which you decide to start your child in kindergarten, it is essential that as a parent you remain involved, and observant. No one knows your child better than you, and chances are that whatever your instincts tell you, they are worth listening to.