Handwriting readiness develops at different rates for every child. It depends on the child's small muscle development, eye-hand coordination, ability to hold writing tools, as well as their ability to recognize letters, shapes, and numbers. Some kids may be ready to write at age 4 others may not be ready until age 6.
It is important that they first master writing readiness skills before handwriting is started. Kids who are taught handwriting before they are ready may become discouraged and develop bad writing habits that are difficult to correct. There are lots of fun activities that can be done to help develop handwriting readiness skills. See Activities to Develop Hand Skills.