Aah ok... doing some math...

DS is in preschool this year.. turning 4 in March. Will be turning 5 in kindy. And turning 6 in year 1. So in Yr 12 he'll be turning 17. That's what I was (but I was in January). I turned 18 after finishing school.

I guess it's hard to predict their level of maturity at that age this far in advance. Personally at that age I don't think the age difference is that big a deal. 6 months can be a big difference in development for a 5yo, but at 17, give or take 6 months doesn't make that much difference IMO. Thinking back to my Yr12, I don't think you could pick those turning 17 from those turning 18. We were all pretty much on the same page in the same school year.

I would think the important thing would be to start them when they are ready, not worrying so much about the later years, cos if they're ready when they start, then they're likely to keep up with each year as it comes. JMO of course