I suspect it is more complicated than you describe, probably a delicate dance between genes, environment, and implicit bias we don't quite fully understand. I'm an autistic person not much younger than Diego who still frequently gets mistaken for a tween and only intersect with your child on the first point and that's because I'm a bit of a hypochondriac and have clinically diagnosed OCD with emetophobia.

As a 2e person, I have been getting in trouble for my what-if thinking and poking holes in adults' logic since my single digit years. A huge part of my day-to-day anxiety consists of grappling with existential and moral thoughts regarding humanity and it's what has drawn me to spend hours studying things like the math behind AI and wetware synthesizers. As a kid, I found the universal gas constant much easier to understand than figuring out whether someone wanted to shake my hand.

As far as habits are concerned, mine leave things to be desired. Sleeping 10 hours happens once in a blue moon for me, especially since I started grad school and my informal bedtime has shifted to about 2:00am. I've had my share of sleep issues practically since I was born. I'm a huge tea drinking fanatic, have the occasional alcoholic beverage, and used to drink almost every day, skip tooth brushing here and there. I also spent the first part of the pandemic so sedentary my joints started to get stiff.

I'd love to see more research on the trend of us looking younger and see if we can rigorously tease apart the factors that lead to this for some of us.