I think if you are concerned then talk to your Kinder teachers. It's not unusual at this stage (during Kinder) to not be interested in writing etc. I work at a Kindergarten (pre-prep) and we have a range of children from ones who can read simple words to kids who can write their names to kids who are just simply not interested, and all of them are ready for prep next year. The only time we would consider keeping a child in Kindergarten rather than moving on to Prep is if emotionally they are not ready to deal with prep and we think it would be in their best interest to stay in Kinder so they build social/emotional skills for one more year. It is also a bit of a process to keep them back for a second year - extra funding, enrollments etc. Talk to your Kinder teachers this week and get their advice - they are probably thinking about transitions by now and will be able to give you an indication on if they have considered your son for a second year of Kinder.

In Melbourne, when is the cut off for Prep? Do they have to be 5 by the end of June that year? Because if yes, he will be the 'average' age. There will be children older and younger and of varying developmental levels. My focus would be on if emotionally he will handle the routines and processes of Prep rather than if he has an interest in writing, but really the best person to answer specific questions about if he is ready is his Kinder teachers. Kinder teachers are often in close contact with Prep teachers, and have a thorough understanding of the schools area and the expectations and limitations of the local schools, especially at this time of the year when considering transitions, and please remember and respect that they are actually registered teachers who have the same qualifications as they school teachers so even though they don't work in a school classroom they do understand what is expected of children when they go to school.
Yeah the cut off in melb is end of april. he's in march. Ill chat to the kindy tomorrow. Yeah didnt realise will be running around if he can do 4 yr old kindy (again)