We sent DS to 3yo kinder last year (he turned 4 in July that year) and he's in 4yo kinder now and will be 5&1/2 when he starts school in Feb.

Due to being in a rural area and needing the numbers to make the program run, we were allowed to send DD who turned 3 in may and missed the cut off by 13 days (cut off was April 30 here in Vic). She will attend 3yo kinder again next year.
She has absolutely THRIVED at 3yo kinder I almost feel terrible that she'll have to do it again, but I know she won't be bored as there's always something to do. She was VERY ready to attend. Her sessions are 2.5 hours, one day a week.