In the beginning: We started when the local schools started.
Later on: We started when I got my shiznat together and we were ready, and I didn't worry about when other people did things. We lived by our own rules!
And then: We started when we finally finished (or abandoned) what came before, even if different subjects started/ended at different times of the year. So if a kid finishes Math 5 in February, start Math 6 in March. They may not finish English 5 until August, and that's fine, too. (Not that my kids were ever even *that* much "on grade level" in so many subjects at once LOL).
And now (ds Junior) We started when he was available (no longer at Summer Intensives, traveling, in Master Classes, etc.).
L (40), wife to C (41), mom to dd C (19) freshman in college and world traveller, and ds K (17) ballet dancer and high school junior, and dd A born April 2015. I'm a homeschool veteran (12 yrs), part-time RN, baby wearer, and breastfeeding mama.