What age do you start preschool/homeschool?

Age 3 for my son, but I try to give my 11 month old motor skill activities to include her.

I have a 9 year old that started homeschool last year, my 6 year old is a Special Needs Child , then after her i have a 3 year old and a 2 year old and because i have to work with my 6 year old they began to show interest they have been doing “School Work” since last year… its surprising how much they have picked up …i have just been working on shapes, colors, ABC’s, this year we are doing “The Solar System” and “ZOO Animals”