Yep. There's variance. I have one kid who can crush online classes sporadically and do tons of heads-down work with minimal supervision and is just six years old.

The other one is almost ten and is on ADHD medication, has borderline personality disorder issues, and while very intelligent, has problems with authority and can't focus online very well.

There's a huge randomness factor that goes into everything, including having kids. It's not deterministic.