Our girls could factor selected quadratics in their heads by the age of 7. They self-taught college calculus at the age of 12. The key was reading, and using linear algebra to teach them arithmetic, solving each problem as if it was a proof with explanation of each step.
Based on what I know about myself, if I had been raised by parents invested in my outcome, I could have probably done grade six within two years and grade 9 in two years and high school in two years.
That’s six years and 12 years old. Possibly, I could have done it faster than that by a year if had parents who were skilled in scholastics.
Do you have a link to any sort of resources or examples of that process?
I forgot just about everything I learned in high school. I hated school. It was like a prison sentence. College was fun but filled with useless courses and time (money). Anything valuable I know I learned on the job.