Many people ask when is a child old enough/ready to write on his own. The following are some of my thoughts on this, based on a discussion with someone about her 9 year old and writing.....
If a child is not developmentally ready to do creative or independent writing, then asking him or her to do so can be an incredibly frustrating experience for that child. It's like people who get little ones to keep journals - how boring is it to keep writing what one had for breakfast?! A 9 year old is only just starting to separate, to stand on his own two feet - to go through that famous 9 year change spoken about in Waldorf circles. If a child is encouraged to write too soon then he or she can wind up feeling that s/he has nothing worthwhile to say and that writing is a waste of time. How exciting it is to witness a child blossom into a writer when she is ready!
By 12 or 13, the child is becoming an adolescent - is able to be somewhat reflective as she considers life and her experiences, has a stronger (and sometimes overpowering!) sense of self - it is out of this that creative writing flows. One has to be fluid in time, comfortable with living into the imagined thoughts of another, able to imagine a variety of situations, to be able to write out of oneself in a creative way - to make up stories that have substance, to imagine into different endings for characters.
Steiner recommended that when children begin to do their own composition at about 9 or 10 that they write about what IS. So examples of that can be simple (and some children will really go far with this) descriptions of say, a trip to the woods or a description of the cat. At 12 or 13 the child might start entering sympathetically into different historical characters (in my Roman history unit study, forinstance, I give several examples where a student could write about witnessing the murder of Julius Caesar or imagine being a soldier crossing the Alps with Hannibal etc etc).
By 14 or 15 the student should be able to write objectively (as I am teaching my social studies students at the Waldorf high school where I teach - I am constantly having to say to them "Your opinion is fine - but it must not be confused with facts!!") and really be comfortable working with various genres of creative writing and poetry.
So back to a 9 year old - I would really focus in having him copy what you write - whether it is your own well written composition or something (verses, quotations etc) from others. By doing this you are laying a firm foundation which he can then base his own future writing on. You will know when he is ready to write his own things - he will demand it!