I would have a standard age and no choice, you have to be five by the 1st Jan and then you can start that year. That is the way it works in UK (although is a year younger) and there really isn't the whole hoo haa there is here. Yes some kids are ready earlier than 5 but you have to have cut off somewhere and based on current system five would make most sense. Having a narrower age band for year group is better IMO. In UK there is always a year and until driving age you never would know whether older or younger in year age was just not a big deal at all. If then school is not the appropriate environment for the majority of five year olds - it should be school that is changed.

Comparing internationally especially with Finland, puts me off any article on subject - as they have free childcare from 8 months and extensive before school options which majority use, plus their success is based on universal access - so without having those systems here you can't emulate them just by changing school age.