What's infantilizing about recognizing that most people attending high school are 13 or older?

Really late reply but exactly this. I said 13 because this was an article about highschool, which for most people starts at 13.

Though, with that said, I don't know what is the youngest age I could generalize it with. Depends so much on the maturity of the child and also how far where you live is from the bus stop. But I think it is safe to say that age is equal to or less than 13.

Well, yes, we do tend to treat children as children.