As a kid I used to read a lot of books (liek 2000+ pages weekly) and I feel like I had an easier time understanding long texts then. It also helped with grades

These days it has been over a decade since I read a "proper" book and sometimes I need to read some passages multiple times for my brain to register what is going on.

It may also has to do with kids having easier time grasping new concepts. I wish they shoved in moar mathz into my brain while I could handle learning new things...
Or maybe it's just that I was reading fun stuff aimed at a younger audience instead of technical textbooks and so