I have a similar problem - my son being born in May 04, and have thought about wanting him to start a whole year later, but have since found out that Ed Qld doesn't allow it.
I'm happy for him to start Prep next year, where hopefully his teachers will keep me updated well on his progress, and if they think he needs to repeat the year then I will be fine with that too. Better to repeat earlier on than later I believe.
He is starting a 4yo kindy program this year (next week) in preparation for prep next year, although he's still only 3.5, so will be one of the youngest there as well...