All 3 of my kids started Preschool (9-3) preschool program within a month of turning 3.
DD1 started NSW Kindergarten at 5yrs 1month.
DD2 started at 5Yrs9months but could have gone a year earlier. She did almost 3years at preschool (1yr 3yr old room and 2 years 4yr old room)
DD3 is in her 2nd year at preschool but still in the 3yr old room and so far is enrolled to start Kindergarten as a 4yr10month old. There is only a very slim chance she will be held back another year.
DS will start preschool at 3yrs too.
I personally find it so much better then a childcare centre that runs a preschool program. Even if it means doing 3years there I would pick it over childcare 100% (except if your needing long day care).